Braxton Hicks?

I'm extremely worried.. I'm only 15 weeks pregnant but I'm pretty sure I'm getting Braxton hicks Contractions. I get KILLER cramps in my lower stomach and lower back to the point of tears. Went to my doctor and they did urine sample and checked my baby's heartbeat which was in 140s but I'm scared. I'm a first time mom, I'm not sure if it's normal to get them this early? Am I just freaking myself out...