Thyroid Stimulating Hormone (TSH) /en.m.wikipedia.org/wiki/Thyroid-stimulating_hormone
You mentioned doubling your Atenolol. How much are you taking now?
You mentioned your blood pressure being low, what is it normally?
My Cardiologist knew I was only taking 1/4 of a 50 mg Atenolol twice a day. My resting pulse was only 60, and I ain't no athlete ;-)
He said I could take more, but I was concerned about
my pulse being too low. He said it would be fine even below 60 as long as I didn't feel dizzy or feel like I was going to pass out while standing. I was having thousands of PVCs per day. My wife was tired of listening to me complain (hey, I don't know any people that can feel them that enjoy them). She convinced me to start taking 1/2 pill twice a day, which was fine with the cardiologist that said I could take 50 mg once per day or 25 mg twice per day. My PVCs fell from thousands per day to hundreds per day. My resting pulse is around 55, and I feel fine.
It will not work for everyone, but it worked for me, at least for the time being ;-)