It's not too early/ They could definitely be braxton hicks. Mine felt like a tightening of my stomach. It would feel hard to the touch, and after a minute or so relax. I'm sure they feel different for everyone, just like labor contractions are different dor everyone.

They can start around 20 wks
the difference is they are eratic, reg contractions have a pattern, get stronger, longer and closer together and don't stop just because you stop what you are doing or start doing something if you are just sitting down
if they are b/h contractions they would probably stop if they started when you were say doing the dishes and you went to sit down, or if they started while you were relaxing and watching tv and stop if you get up and walk around a little, and they come and go without having a pattern one could be strong and then they get weak, you can have a longer one then some short ones, one that hurts pretty bad and some that don't

hope I didn't write that too confusingly!!!