Hi Dr, I'm 33yrs Turning 34 This Year. I've Noticed

Hi Dr, I'm 33yrs Turning 34 this year. I've noticed that when I'm at the gym, especially when I focus and concentrate more on my stomach muscle abbes (six pack). I experience internal pains. I've had a medical operation before via my appendicitis (removed 12years).

So what could be the cause of my problem? And how long does your appendix heal? Once removed via an appendicitis medical operation?