Painful Braxton hicks contractions?

Brit • One and done so I'll be a FTM forever.
I keep seeing posts about painful Braxton hicks contractions and I'm wondering when these start for most people. I rarely notice them right now and if I do it's just by fluke that I touch my stomach while one is happening and it feels super firm. So I'm curious, when should I expect this to change? Thanks :-)