I think it sounds like your adrenals are struggling. I had similar issues with not being able to tolerate exercise and ended up supplementing a couple things to help my cortisol levels. Check out the info on Stop the Thyroid Madness related to adrenals. I've also found lots of good info on the facebook group Adrenal Fatigue and Thyroid Care. I'm still working on adjusting everything (I also have Hashis), but I've definitely found that thyroid/adrenal stuff is interrelated, so increasing thyroid meds may be helpful.