Ive only had two occassions so far when I had a contraction, and it was only one and it wasn't very painful, it was a bit, but more a tightening pressure.
Now... Ive also had extrememly bad stretching pains and they have lasted hours... Everything is so effin' so you can even sleep or get comfortable

But for me this is more my whole stomach and especially the sides because of the ligaments that are stretching.