I M Very Much Confused Dr ..i Had My Menses

i m very much confused dr ..i had my menses on 28 march after dis i had sex wid my bf on 21 april we did it wid condom..but in april i dnt hv my periods..i checked on 7 may d test was negative den i again test on 12 may it was negative..im taking resgestrone form last 4 days..im confused whether im pregnant or i hv sm prob with my periods..n in how many days i will hv my periods