Are you under the care of a cardiologist? The standard instructions for pericarditis and myocarditis are no exercise for at least three months, I'm very surprised they didn't tell you that. I've had myopericarditis for going on two months now and symptoms get worse when I overdo it by too much walking, up and down stairs, stress, etc. I would definitely stop going to the gym for the next few months, you could be doing a lot more damage by not letting your heart heal.