Belly ache or contractions?

I'm a FTM entering my 37th week tomorrow and I can't believe how close I am already. I had my routine OB appointment this morning and everything seemed fine. I had noticed my belly being harder than normal the past 2 days but she assured me it could just be BH contractions. Well its been 4 hours since my appointment and I've come down with what feels like a bad tummy ache but also my mid to lower back is hurting too. My belly is very firm.

Is this what beginning contractions feel like or am I just having a common tummy ache?