periods!

So my period is kinda screwed up. It will be on time for 2 months. Then decide that it's going to be late anywhere between 5-15 days. Ill have my period on the 5th or 6th for 2 months and then I'll have it on the 15/16 the following 2 months. Last month it was normal but now I'm going on 6 days late and was wondering if this is normal? I'm just sick and tired of not knowing. It's always been inconsistent, would birth control help at all?