Help! Not sure what to do

My last period was on March 5th-9th. I haven't had any symptoms of my period coming and I'm starting to get a bit worried. I should of got it April 5th and May 5th. I've taken two pregnancy tests that both came up negative and within a week apart from each other. I did take plan b in march and I know it messes your cycle up sometimes. Should I be worried or am I over reacting? Any advice?