This sounds like it can be a lot of different things at the same time, which will make it hard to diagnose. My wife has a similar problem with pain and has very weak wrists and ankles, or, she believes she does and therefore does. But she doesn't have any of the other things. Some people don't show muscle gain, they just don't. Others get incredibly quick increase in muscle size. My wife got me into the gym lifting weights, it wasn't something I did. She had been doing it for a long time, but doesn't look like it. I started getting much larger muscles right away. I have no idea why this is. But it just is. But muscle definition is just cosmetic, some of the strongest people on Earth don't look at all cut, they often look overweight and fleshy and then you see them pulling a truck. I'd definitely look into the above,. but I'd also look into everything else, as well, including the mental side of things, as the list you have put up here seems to go in different directions.
Interesting. My son was diagnosed with something called sensory integration disorder. He's sensitive to taste, touch, smell, light, distraction, stress and has trouble with motor skills at times, sleep and anxiety. Sound familiar? It involves the nervous system and how the brain communicates through the nerves. The wrong signals get sent at times. My son did occupational therapy for 6 years with a recent tune up (diagnosed very young and is now a teenager). Things that help are what they call heavy work input. This is something like lifting some weights (a 5 pound dumbell, for example but even carrying heavy laundry basket, some books across the room, pushing something heavy across the floor like a couch or chair), things like swimming which has deep pressure and also work so is really soothing and healing to the nervous system, laying on the floor face down and gently pushing pillows onto them helps. But it's ongoing. Have to incorporate it into the routine. Chewing thick bubble gum or eating licorice gives the heavy work input, believe it or not. Any jumping activity like jumping jacks or a little at home, small exercise trampoline helps. My son has touch issues and did brush therapy. It worked really well. They use (and we did it at home when they taught us) a hospital baby hair brush or scrub brush (both work, they are plastic with soft bristles, does not look like a hair brush Here's a link (copy and paste) to what I'm talking about https://specialsupplies.com/sensory-brushes?_vsrefdom=adwords&gclid=Cj0KCQjw6575BRCQARIsAMp-ksNB79ry_2tSkXA00q--ZNtPNar2dB3W4ILlanWiuXzNIj9gU_GB0loaAl84EALw_wcB ) It's called the wilbarger protocol. It definitely helped desensitize my son to touch.
I'm happy to talk more about this for you, we've been dealing with it for a decade.