Why Does My Pregnancy Test Shows Negative Results After Having Unprotected Sex And Missed Periods ?

:) Good Day Doc, i missed my periods for almost 2 months already my last period was on March 19, 2001 ends March 23,2011 My periods was regular so I expect to come my period on April 23 onwards.. but until now May 31,2011 my periods was not come but i don t have any symptoms of being pregnant . I Had unprotected sex 4 times happened on April 20,27,28 and May 28,2011 on my date stated above it s possible to get me pregnant? but i have done many test like pregnancy test and also SERUM but the result was negative i took a test on may 21,2011 but now i did not check again. what is the best that i can do to check if im pregnant or not? though i had negative result.. Im 21 years old and my boy friend started to asked if my periods was come? Now, everytime i moved i feel my periods will come any moment due to i feel wet and i flew white means.. please help me what should i do?