Contractions are different for everyone, some only have back contractions for some it's period like cramps. Your body is prepping for labor so your going to have Braxton hicks on and off. My dr says When you can't walk or talk through them and they last for two hours is when you need to go in or if your water breaks. Hope this help, good luck.
Mine for both pregnancies have started on the bottom similar to bad period cramps. Braxton pains are when all ur belly get hard good luck