Braxton hicks vs contractions

I am 27 weeks and feel like I get Braxton hicks/contractions extremely often! Even when I'm just sitting down. But pretty much any time I get up from sitting or start walking around, I get them. Also, is it normal for them to feel like menstrual cramps? Almost like I have a heavy period? I don't remember this happening so often and early with my last two pregnancies, or that I felt so uncomfortable.