Did/do you have creaky joints? My knees sound like skeletons getting freaky when I walk. It's loud. And kind of embarassing.
I thought, well, I am carrying extra weight, so maybe that's it, but (in an related, but only a little) I found out why my pants don't fit, and apparently I've lost an add'l 7 lbs. I'm only 18 lbs away from my Pre-pregnancy weight (but I still have about 50 lbs to lose after that.)
So, I'm still heavier than before pregnancy, but I would have thought that my joints would have stopped creaking and cracking so much, you know?
But I would go and get your thyroid checked out. You may have Hashi's, it's sounding like you could possibly be going through periods of hyper and hypothyroid which are symptoms of the disease. Especially if weight is hard to lose and then you drop 7lbs like nothing, without changing your eating/exercise habits.
I should note, I am not a doctor, nor do I play one on tv so take any of my "advice" with a grain of salt, LOL.