It may well be pre-term labour or just a case of gastro.
When I went into pre-term labour, the abdo pain I got was like a really bad period pain, but it also felt like a string between breast bone and pelvis was being pulled with each contraction doubling me over, these pains came at 2 hr regular intervals. I didn't have any diarhoea or discharge.

I suggest if you are concerned call the hospital and go in to get checked out.