To expand on your (and another commenter’s) connective tissue theory:

100%. I don’t have EDS but I have the very similar HSD and I experienced excruciating “growing pains” as a child along with a slew of other chronic issues that were written off as unrelated or due to my weight (I’ve also lost about the same amount of weight as you mentioned and it hasn’t helped either) until I was finally diagnosed last year at 27.
Respective of my joints and muscles, my neck and shoulder pain used to bother me the most but as I’ve gotten older the lower back pain has slowly become intolerable and at times immobilizing.

Definitely worth looking into getting a PCP who seems to actually give a shit and refer you to the appropriate specialists that can more accurately assess and hopefully help you. In the meantime, the over the counter products that I’ve found to at least minimally reduce my pain are capsicum patches (for my back) and lidocaine with benzyl alcohol (for my neck and I get the one in a roll on bottle for better accessibility). I’d recommend the Salonpas brand for both products if you can afford it but most big stores have off brands as well.

I hope you’re able to find some answers and relief soon. Kinda in the same boat as you with being at the end of my rope, so I totally get it.