First pregnancy I got them about 25 weeks, but this time I was feeling them at 20 weeks, it sounds ridiculus but I recognized the tightening feeling and have been getting them ever since. More so on days when I don't drink enough water or have been house cleaning a little more than normal.
It doesn't sound ridiculous - i think I was getting them that early too this time around! My belly kept going taught and achey for a few minutes and would then relax - but even with ths being pg2, it took me until I was around 28 weeks to get the lightbulb moment and realise that I'd been getting BH for weeks!!