HELP! early labor? 33 weeks

All of a sudden about 40 minutes ago I got a sudden horrible pain in my lower back. About ten minutes after it went around to my stomach and now my stomach is cramping. I'm not constipated or anything, and it's a very strong ache. I feel like I'm going to puke also. I'm only 33 weeks and don't wanna go into labor yet. How do I know if they're contractions? It seems to just be one long ache that gets worse sometimes :(