I had protected sex(condom) on day 30 from last period,day 36 today,still no periods. my cycle is very erratic. am i pregnant or sex messed my cycle?

Can do a preg. test: Have faith that the condom worked fine. If periods are not regular, it is not accurate to use a "missed period" as a sign of pregnancy. Home pregnancy tests are very accurate and not affected by foods, herbs, common illnesses, sexually transmitted diseases, or medications. A correctly done urine test gives a reliable result 3 weeks after sex (3 weeks after when conception might have happened).