21 wks Braxton Hicks contractions?? **TMI**

This morning, I woke up with intense back pain. I thought it might have been from laying on my back for an extended period of time last night, but it doesn't normally bother me. I tried elevating my head and laying on my left side to alleviate the pain, but the longer I laid in bed I started to feel sick. So I went to the bathroom and tried doin my business, but I felt a little constipated so I thought maybe that's why my back hurt. But the pain just kept getting worse, and it started to feel like menstrual cramps. Like REALLY bad. To the point I was on the verge of tears. They came and went in waves too, so for a minute or two I'd have cramps, then another minute they'd relax. This went on for about 15 mins. Is this Braxton Hicks contractions??? I'm currently 21 weeks pregnant, so I didn't know when they typically start, if at all, in some women. I have felt fine the rest of the day, but I'm still really curious and wondering if I should ask my doctor (I go for my full anatomy scan in two days).