Contractions..???

I'm a FTM and honestly completely clueless. What do contractions feel like? I've been getting a kind of sharp tightening period like cramp in  my lower back and hips.  I've been getting Braxton hicks all day but this is different I think?? 
I try timing it but it's hard because although the start to the pain is obvious, it just fades off until it starts again. I guess my only plan now is to see if it gets worse. It is painful but I'm not screaming out or anything so I'm not sure if it's contractions or not. I'm 38 weeks tomorrow. I don't think my baby would come this early as I am a FTM so I'm very hesitant about driving 1 hr to the hospital just to be sent home. Could it just be my hips widening?