One thing that should put you at ease...Lower left quadrant pain in the colon is one of the most common symptoms of IBS. And, as you've already noticed, STRESS and ANXIETY make your IBS act worse than it would otherwise.
I would ask either your PCP or your GI doctor about an antispadmodic medication for IBS called Bentyl (Dicyclomine). Just be sure you have the doctor explain what the medication is and what the side effects are. I have General Anxiety Disorder (GAD) and have found that the sedating effects from the Bentyl are actually helpful when I'm undergoing high anxiety and stress. Not everyone with IBS likes Bentyl because it is so sedating, but I find that it is very helpful for me. If you want an antispasmodic that is less sedating, there is a sublingual medication called Hyocyamine that you can ask your doctor about. I tried Hyocyamine and it wasn't effective for me. One thing you need to be aware of, though, with the Bentyl--you need to take periodic breaks from taking the medication, because long-term use is ill-advised. You can ask your doctor to explain this, but this information is also found in the patient information leaflet that comes with the medication. Of course, now days you can just use Google to find the information about either one of these medications, too.
I was diagnosed right around the time when I was your age, too. This was actually before any tests were even done to rule anything else out. Given my case history, the GI I saw all those years ago was able to diagnose me as having IBS, which I most likely have had my entire life. Naturally, I have since had the scopes done--all of which showed negative for any other condition that would cause the symptoms I was having. The GI I saw when I was your age was right on the money.
I would recommend seeing your PCP about getting a referral to see a GI. Although, I can tell you what the GI will recommend, since I have the same kind of IBS as you described ^. I would also recommend seeing a naturopath at the same time. Naturopaths are very good at helping people with IBS get their IBS under better control, because the best way of controlling IBS is through your diet. Many of us have food sensitivities that we're unaware of. A naturopath will help guide you through what is referred to as an Elimination Diet. Figuring out your food sensitivities will help you get some control of your IBS.
And, as you've already discovered, we carry our emotions in our gut, so IBS is affected by the stress and anxiety we experience. So, it's a very good idea to do what you can to keep your stress levels down. People with IBS are often prescribed anti-anxiety medications, such as SSRI medications or trycyclides, since this often helps calm the spasming colon. If you're a coffee drinker, you will need to cut down or eliminate your coffee intake if and when you're feeling a lot of stress and anxiety, since the coffee will only serve to aggravate the stress.
The things that a conventional GI will recommend for someone who has IBS that is predominantly constipation are dietary fiber, such as Metamucil or Citricel, a stool softener, such as Colace or Dulcolax (both are actually the same active ingredient) and a laxative, such as MiraLax. I am using these suggestions in addition to the recommendations from my naturopath to control my IBS. This kind of approach to medicine is referred to as "integrative medicine" and uses conventional medicine in combination with natural medicine, using what is best for each individual patient. I developed sensitivities to certain medications, so integrative medicine works best f me.
I'm also petrified it could be Diverticulitis, don't know why, i really should stop looking things up on the internet, it plays havock with my paranoia.
I think it cos the area where it happens mainly is exactly where i get my spasms/cramping, but it's not severe, just quite sharp for a few minutes or a bit longer. But i have suffered from constipation the last 6-8 months on and off but it's more regular now. But i know if i'm not going to the toilet regulary i will get a build up so i more than likely will get cramping in that area of my colon where the pressure is.