Go and get checked out hun, just to put your mind at rest as much as anything.
Not to scare you, but our son was born at 28 weeks after having mild cramps, escalating to bigger cramps and all in the back. Even the abulance drivers and the obstetricians didn't think Sal was in labour until they checked and found her 3cms dilated and he was born less than three hours after that. Premmie's have good odds at 26 weeks, if they are born in the right place ie in a maternity hospital set up to cater for that, so perhaps a trip to the doctors/emergency room wouldn't be a bad idea.
Good luck!