puzzled about periods

Hi, my name is Allie I am 23 and I have 3 children. my periods are normaly on track but this time it wasn't. My last period was may 7th and I was suposed to start on June 1rst but my period never came. I took a pregnancy test on June 2nd like the doctor wanted but it was negative and then we did a pregnancy test at the doctors office June 4th but it says I am negative I don't nderstand why I have missed my period. Could I be pregnant or could something be wrong? Please help need advice, thankyou.