First of all lets start with the fact that I am male :) And yes I realise that this post is long, but bare with it.
This all started three years ago and made its presence felt as an area of tension, around the bottom of where you'd say the bladder is and forward towards the front end of the pelvis, but behind the pubic bone. To feel the tension I'd have to lie down on my back, it wasn't painful, but just felt as if something was being pulled tight. All of a sudden however whatever it was that was being pulled tight let go, something moved and it felt as if something inside of me had ripped and I was left in agonising pain.
The pain itself felt/feels much like what the people in the linked thread are describing. However for me the pain is persistent rather then intermittent.
I also have a feeling now that there is a lot of referred pain involved. At the time I also mentioned to my GP that it felt like there was this thin string that stretched from my navel down to the bottom of my pelvis and that it felt as if it was being pulled tight and that this is what was causing the pain. As a result of this he referred me to Gastro where I had an examination, then an ultra sound and finally a CT scan. All of these came up negative, but by the time all of this had taken place the pain itself had become significantly better and appeared to be on the mend so it was left at that.
Both my GP and myself both felt at the time (and still do feel) that the pain is probably caused by a physical injury of some sort as the pain is very positional. When bad, every position is uncomfortable, but others are unbearable, such as lying flat on my back (this feels like the previously ripped tissue is being pulled on again and causes severe discomfort). But when the pain is better, as if it's healing itself to a certain degree, some positions are completely painless, whereas if I try and lie down...However if I take my time in lying down (this takes hours) the pain itself is far less severe. Kind of like I go from sitting to lying but in small controlled steps, going further into a lying down position with each step and letting whatever it is that's being stretched get comfortable with each step. So whatever it is that's damage is capable of extending that far but just cannot do it in one go - kind of like how you can end up doing the splits painlessly after stretching, but without you'd do some serious damage.
As I said this appeared to get better and to a certain degree it felt like it had, progress was extremely slow (18months), but over time whatever it was that was damaged felt as if it was healing. At its best I could lie down in bed on my back without feeling any discomfort or tension, but what I thought I was feeling was perhaps not quite as it should have been. I was on 25mg of amitriptyline/day at the time and had been for most of the duration of the injury, so when I thought it was better it wasn't quite there (I know the amitrip helps with the pain quite significantly). Subsequently I picked up a bag of something heavy (25kg) and supported it on my lower abdomen. I have always had strong stomach muscles so supporting the weight itself wasn't a problem and in doing so I didn't really feel any great discomfort, but a day later and the pain started to return and did so in earnest. I have no doubt in my mind that the picking up of the heavy weight was what caused the symptoms to get worse as physical activity has always been the number 1 trigger for making things worsen. The stomach muscles themselves aren't the problem, only I am sure that when you pick something that heavy up and support it where I did that it puts a lot of strain on the pelvic support muscles and ligaments too.
If I get back to the referred pain part of this though I believe that the actual injury sustained is down at the bottom of the pelvis and that the painful 'string' pulling sensation from the groin to the navel is in fact completely referred pain. The problem is down below (and is indeed stressed when lying down), but due to some people sharing nerve pathways between the navel and the groin (the shooting sensation one can create from navel > penis when one 'tweaks' their belly button etc) the pain/damage in the groin makes itself felt within the navel region and this causes confusion. I know that the pain feels at its worse when lying down and trying to 'reach' up for something, so one naturally assumes that something is perhaps being pulled between the navel and the pelvis, but this could perhaps be misleading.
I can gently manipulate the area between my navel and the pubic region and it doesn't cause any gross discomfort. If something was indeed being pulled tight between this region you'd expect it to cause some significant increase in pain (because lets face it the pain can be extreme), but it does not. I can however manipulate the area just around the navel oh so very gently with just one finger and cause an increase in discomfort. I believe the navel side of things is completely referred pain and although very real in how uncomfortable it is, it is in fact extremely misleading when it comes to people complaining about a pain that feels like the title implies. Doctors don't know what to do with it because it makes no sense, there are no connective structures that run from the navel to the lower groin, there are however lots of things down near the pelvic floor and above it that can be the cause of pain and then there are lots of nerves.
In my case the pain is generally always there, and I believe it to be muscular/skeletal in nature. In the other peoples' cases it could very well be that they have in fact strained a muscle a little, caused some minor damage to something within the pelvis through daily activity or a workout and this is what they would normally feel, but because the referred pain is actually worse then the real pain it throws off on making any kind of diagnosis. Lying down or stretching up naturally puts extra strain on all areas of the body (including stimulating nerves) and normally this doesn't result in any pain because the body is flexible and well designed against the internal organs/structures moving about. But if something is damaged or mildly inflamed, going to a positional extreme could cause an increase in discomfort because something is being stressed.
Following on from the 25kg lift the pain got worse and then, very slowly, started to get better, however once again boom it gets worse. This seems almost cyclic with a very slow repair rate and it taking a very short time (although not instant) to get worse.
So far I have had another abdominal ultrasound and another CT scan. Once again nothing was really found and I did try and have an MRI scan, but that was a complete failure, 40 minutes flat on my back with heavy sensors pushing down on my lower abdomen? I didn't even last 5 minutes. I have also had a digital rectal exam where my prostate was found to be fine.