Braxton hicks???

I don't know what I'm feeling...but it really isn't pleasant. When can Braxton hicks start and what do they feel like ?? can somebody in 20th - 21st week get them?? Like this is a constant pain that feels like it's tightening and then it'll relax for a while then happen again...but I'm having multiple!! Last night I felt so sick, it woke me up and I didn't actually get sick but I'm surprised I fell back asleep it was that bad...these feel like really terrible period cramps that go away for a minute but they keep coming back and having several....definitely feel like there's been more than 6 an hour I'm counting them right