What's happened to my body?

I've been having a problem going to the gym consistently due to the fact that my body (specifically the part I worked out) is in severe pain, but only 2~3 days AFTER the workout session, which throws my schedule off completely and I end up tired for half a week trying to recover

For context I used to workout regularly until Covid, then I went to college so I didn't have time/motivation anymore but my body has been getting really weak so this is the 2nd summer I'm attempting to get back into it but it's not working...

I'm 23M/79kg and because I try to atleast have an okay diet due to my gastric problems (I'm also sensitive to weight gain) I have an okay body shape, neither fat or skinny.

I'm not sure what I'm doing wrong, I'm taking in around the same amount of protein as I used to before I stopped and also I'm following the exact same workout routine which was definitely not heavy, and I've cut it down even more

EDIT: Perhaps might be important context; I feel like my weaknesses starting happening after due to the panic attacks/severe palpitations I suffered for over a year, but they have stopped almost a year ago at this point and I've done check-ups many times and everything seems to point to okay (except my gastric issues)

TL;DR Go gym once, muscles sore all week even though it wasn't like that before