Last mth i had two periods this month i have yet to have one i took 3 pg test but all neg, what could be wrong?

i usually get my period around the first of the month and last month i did but then i also had a unexpected one kind of in the middle of the month also, and now it is july and i have yet to have one. i have taken three pg test and all have came out negative, i thought i could of been pregnant but now i dont know. my period schedule hasnt changed since the first time i got it, i just dont know what to think...