Late on Period by almost 60 days

I have the chance of having twins or triplets. (My dad is an identical twin, twins run on my dads mothers side of the family). Anyways, I have gone off of birth control in May because my husband and I are trying to conceive. i had a period in June but have yet to have any others. I am a few days shy of 60 days late on my period but am having negative pregnancy test results. (Blood and Urine). I have read that sometimes when carrying twins one can have negative pregnancy results until about 11 weeks. Any insight is great!