I would lean more toward it being constipation/gas, but you never know.
A while back, after my 1st abdominal surgery, I had what you're describing (tightness/pain). I thought it was the problem coming back. I headed to the ER, had test & Xrays done, only to have it turn out to be gas.
I tend to think that because of my strange experience, but you might want to get it checked out just to be on the safe side.
The only thing necessary for the triumph of evil is for good men to do nothing.
~ Edmund Burke