It could indeed be labor. If they feel like menstrual cramps then chances are it's the beginning stages of labor. With my first I began laboring at approximately 1am with slight menstrual like cramps, that came and went I was able to go to sleep thinking maybe it was early labor, then I woke up at 5:30am with the pains only much stronger and closer together lasting about a minute each coming every 2-3mins. I called my friend to ask her if it was labor and she told me it was. So I went to the hospital after first eating breakfast and when they checked my cervix I was 5cms dilated.. Needless to say, it was labor and my son was born at 1:45pm.
If they they come n go for an hour then call you midwife or gp...