Braxton hicks... When did yours start?

So I'm 25 weeks pregnant on Sunday and for the last couple days I have been having period/poo like cramps. My belly tightened and I had no idea what they we're so I just kept assuming that I was fighting off a bug. At last I asked over social media and my friend called me saying they sound like braxton Hicks and hers were the same thing. Comments and experiences would be great to hear :) thanks!