My heart rate has always been like 60, but because of anxiety i never know, sometimes high and sometimes low....
I am not aware of any causal relationship between a HR in the 48-58 range and being tired, rest HR assumed. Some who normally have a resting HR of 70, say, might feel dizzy when standing with a rate in the upper 40s, and it could be a sign of trouble.
If you haven't had a change in, or new medications, then it isn't caused, I think, by medications.
What had your resting HR been prior to the last few months?