Help, doctors have given up trying to figure out what’s wrong!

I’m 52, 18 years post menopausal. For about a year and a half to two years, I’ve been having issues and, at this point, all the doctors I’ve seen have either given up or focused on the one thing I know it isn’t.
I’ve had massive weight gain even though I don’t eat a lot and I eat healthy foods most of the time. I’ve also had issues with being tired all the time, my hair stopped growing for a time, my nails are brittle and I’m having trouble regulating my temperature (always running hot and cold). I’m also on medication for bipolar disorder. I’ve had GPs blame it on me overeating and eating the wrong foods and they don’t believe my husband or I when we tell them I don’t do either of those things. I had thyroid testing and my T4 came back low for normal standards (the lab my doctors use have a different set of numbers that are much lower, however). I explained to my GP that when my levels were .85-.9, I felt better. Now they’re at the low end, .6-.64 (normal by the lab they use) and I feel awful. He agreed to put me on levothyroxin and I was feeling a bit better for 6 months before I felt lousy again. He did bloodwork and found my TSH dropped and my T4 hasn’t gone higher. He told me to stop the med and retest in a month. My TSH went back to normal levels but my T4 dropped again. So I saw an endocrinologist. She tested a lot more than my GP and said they go by TSH, not T4. They did a cortisol test. Twice it came back low so they did the stimulation test and it came out normal. So they all say I’m fine, but nothing has changed and I can’t lose weight no matter what I do. I know it’s not my psych meds, I’ve been on them forever with no issues with these particular ones. So if I’m not eating too much or the wrong things and it’s not my meds… What is it?
Recently I’ve been getting more headaches than usual and they’re trying pretty bad. I know the endocrinologist stated that I had a traumatic brain injury from a car accident I had at 19 (I don’t think it was that bad, but she did). She didn’t think that messed up anything, so I don’t think that’s it.
At this point, I’ve gained so much that I don’t want to leave my house because I’m embarrassed by how I look. I’ve always been very thin and didn’t even gain much with two pregnancies. I’m so uncomfortable… Being so overweight hurts my joints so much as well as my feet. At night, when I lay down on the sofa to watch tv, I can’t lay comfortably because I can feel the fat inside gushing up into places and it hurts. I have a hard time laying down at night because it’s so painful, these inner fat rolls. Worse, thigh my legs don’t look heavier, I can’t kneel and rest back on my calves because it’s incredibly painful. It feels as if they’re swollen but they’re not.
I’m at a loss and I don’t know what to do anymore. My doctors and those I’ve gone to for second opinions have given up. All they want to do is prescribe a GLP1, but I don’t trust those and I don’t see what it would help as I don’t have a large appetite. They’re all focusing on my eating habits and that’s not the issue. I can’t even exercise anymore to try and lose weight that way because my feet and hips hurt so badly when I take a short walk because of the weight gain.
Does anyone have any ideas? I’m open to entertain any thought at this point.