I use to get Braxton hicks starting around 24 weeks, towards the very end of pregnancy I called L&D A LOT! it's more or less the tightening in your belly and then goes away, however real contractions will be different! You will be able to tell if its the real thing..pressure is also a symptom with real contractions..timing them is also good to know!
I have had them since about 23-24wks. Now I get them and they are actually timeable if I pay attention to them. My belly will get tight for a min or so than goes away for 5 mins and comes back. I at least have them a couple times a day. Glad they aren't painful for me.