Are you on beta blockers? Everyone is different but a lot of people find them hard to tolerate energy-wise. They kinda have the effect of not letting your heart rate get above a certain point and this makes it very difficult to work out.
My heart rate never went over 60 throughout my whole life usually in the 50's unless I was nervous, had a panic attack, a fever or exercised. I have/had all kinds of energy.
I was put on Beta Blockers at one time for high BP and I was so fatigue I couldn't do anything. But my heartrate due to the beta blockers had dropped to 30bpm and the Cardiologist I was referred to took me off the beta blockers immediately.
What was your heartrate before the meds?
I am on Beta Blockers to slow my heart rate down, this was because I have been fitted with a Septal Occluder to seal a hole in the heart.
My geart rate on Betaloc was around 60bpm, I recently had to change my doctor who put me on Atenolol my heart rate is now between 50 and 55, I do not get any side effects, eg dizziness and although I get quite tired late at night my energy levels seem to be quite good, my age is 64.
I must admit I dont have the stamina to do some things that I was able to do before I was put on Beta Blockers but I am now 9 years older than I was before I started taking them,
I can however do a days work and I walk most days to keep the weight off, as soon as my weight gets to high I do feel more lethargic.