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.