I have protected sex and my boyfriend didnt cum. im 3 days late on my period. whats wrong with me?

You're nervous: Protected sex implies you used a condom or are on birth control. In either case pregnancy would be unlikely. Some normal women occasionally skip a cycle or two. I would not assume you are pregnant. Over the counter urine pregnancy tests can be found at many convenience stores. They would be positive if this delay is due to pregnancy.