Heart rate unusually high during exercise after coronavirus.?

Had the infection way back in April and feel more or less back to normal again after being sick for a few months. Only problem is that every time I attempt to gym my heart rate quickly shoots up to almost dangerous levels. I have to stop after working out just a few minutes as I start to feel light headed and nauseous. I've tried warning up with light cardio and it helps a little but I can't gym with nearly the same intensity as before.

I had a EKG done which showed nothing out of the ordinary. My heart rate only goes up to very high levels when lifting weights not so much with cardio. My doctor said I seem to be fine but no further testing like x-rays or anything were done as they did not deem it necessary.

Why is this happening and will I return to normal again?