Hi there. You are only 23 and experiencing this and that is strange. You said it started with an intense leg workout. Were you a regular at the gym before this?

I've read some of the comments on long covid. Long covid is one strange affliction and it seems little is known about it. I'd certainly ask your Dr, although you've probably done this.

It could also be sciatica, or something messing with the nerves in the spinal canal that affect the legs. Although you'd experience pain and numbness and you don't mention that.

As for the cortisone shot - not sure where the shot would be placed? An epidural, in the lumbar spine? That seems the most likely.

I'm sorry I don't have any new suggestions for you. I do wish you all the best in figuring this out. Hiring a trainer is a decent idea. I'm just not sure that gets to the underlying problem.