Heart symptoms worse even with beta blocker-what is this?

I have been on a beta blocker for a year now for tachycardia. Dr didn't investigate the cause other than doing a holter monitor and EKG several times. It was also blamed on my thyroid before they took half of it out due to nodules...none of these things fit the cause for the fast heart rate and nothing improves it (not even weight loss). The symptoms I get are heart pounding (palipitations) tingling in both hands, short of breath, clammy- like a cold sweat, confusion and extreme exhaustion. It seems to be happening more frequently too. These symptoms were not all present when I first started taking the beta blockers 1 year ago. One day last week, I forgot to take the med and this happened so I blamed it on that. The next time it happened exactly the same and I had already taken the beta blocker hours before. I also have an autoimmune disease so I thought it was yet another symptom from that but wanted to ask anyway to see if other's have the same symptoms.