So it turns out what I was feeling were not Braxton Hicks. I went in for my normal appointment and they said my labs from last week showed I have a bladder infection! I have no other symptoms (well, other than peeing all the time, but I chalk that up to pregnancy). They said my bladder muscle was probably spasm-ing from the infection, not BH.
On another note, I had a scare. They tried to find the hb and couldn't, so they did an u/s. Everything was fine and normal, but man was I freaking out during that 10 minutes before the u/s! I did get to see baby kicking and moving around, which was an unexpected delight.