Contractions??

How early can you get actual contractions, not braxton hick contractions?? And what do they feel like? I get pain down there and I was told that was a braxton hick contractions. Tonight at work I got a sudden rush of like bad cramping and I wasn't sure if this was also braxton hicks or if this was a legit contraction. I plan on calling my OB tomorrow and setting up an appt because I feel like its way to early to get contractions at 27w. I've also been feeling pressure from my belly button down.