Is it possible to have only one or two real contractions at a time, or are all of the early ones still considered Braxton-Hicks?

I ask because I am occasionally getting what feel like period cramps and nausea for about 30 seconds-1 minute, then they disappear. It happened once last Friday, and once again last night. The first time, I definitely felt my belly getting tight, and yesterday, I just got overwhelmingly nauseous for a minute or so, then it was gone. Each time, I've only had one, so I wasn't too concerned, but I am curious. Are these just really strong BH, or is it possible to have legitimate contractions for weeks before going into labor? I'm 31w 1d, and at my appointment on Monday, my cervix was closed. I figure I'll ask again when I go in next week, but I wondered what other bees' experiences had been.

Thanks!