I'd say do check with your doctor, but I have a couple of thoughts. Again, I'm not banded yet, so I can't say I know exactly what you all are experiencing from weight loss. However, last fall I was sent to a rheumatologist because I had pain in weird places. My joints ached, my skin hurt and I was exhausted. Firm pressure felt good, but light pressure hurt. The worst pain was muscle pain. My biceps and forearm muscles felt like I was in a weightlifting marathon and I didn't lift weights. The arm pain would stop if I would lay on my arms, so I tossed and turned all freaking night. Sometimes it would get so bad I would just get up and work or watch TV. I even had to give up knitting. Heavy quilts on the bed helped. I had 3 quilts and a bedspread. I could barely turn over, but once I got settled, the pressure helped me sleep.
After my exam by the rehum doc, she said she was going to do all the normal tests for lupus, fibromyalgia, etc., but she was also going to test my vitamin D level. Everything came back normal but the vitamin D. I was extremely low and it was right at the end of summer, and I had been outside some pretty much everyday. I can't tell you how much different I felt after being on vitamin D. She put me on the rx version. I had it tested again recently and it's still not where they would like it, but it's much better, and I'm much better. So I would suggest reading up on vitamin D and getting your levels checked. I also started taking a B complex because Bs are the nerve vitamins - especially B6. The hand surgeon I typed for always put his carpal tunnel patients on B6.
The other thing that comes to mind is that our nerves are used to being very well insulated with fat, and the sciatic nerves run through each buttock and down the hips and legs. I wonder if it could be a temporary form of neuralgia or neuritis from the nerves having less insulation. Also, cold air makes people with nerve pain have increased pain. People were talking yesterday about bands feeling tighter in summer and I wondered if that could be due to increased cold fluid intake. And it makes me wonder of some of the aches could be exacerbated by air conditioning.
Just something to think about that helped me through some major aches and pains.