Contractions?

First time mom here, not really sure what the feeling of a contraction is supposed to feel like or any types of differences, but kind of have a general idea sorta. It hasn't been happening often, but surely enough the past 1-2wks. I am 33wks4days and I could possibly be confusing it with Braxton hicks. My description of it is like the beginning of an orgasm down below but one wrong move and it's painful, certainly not pleasurable. I have to stay put in that position if I'm laying in bed or not walk as fast if I'm out and about until the pain passes and I can than continue to carry on just like a minute or two before it started. Any ideas? Thanks!