Braxton or preterm..?

I'm almost 36 weeks and having really bad abdominal pain/cramps. For some reason I don't think it's braxton cause of how painful it is.. They're irregular , last for maybe 15 seconds, and I had three of these contractions last night at work. Braxton Hicks isn't supposed to get worse when you're moving around but for me it does. I don't know what this is but it's painful and seems like as each day passes they get stronger and stronger.