Question About False Negatives on Pregnancy Tests?

Ive been on the Birth control pill for four months. At one point this month I was Prescribed an antbiotic and only took two pills when I remebered that they can cancel out the pill. So I stopped them. Then in the second week of my pill pack I had some breakthrough bleeding which lasted about a week. At times it was heavy but most of the time just spotting. I called my OBGYN and they advised me too take a pregnancy test which I did and was negative...All my friends keep asking me if Im pregnant because i do look bloated in my belly...But I also had a baby 7months ago and I just chucked it up to bloating since my period was super weird this month. Ive never had any irregular periods and when i took my prego test with my son i tested 5days b4 my missed period and got a clear +. Wouldnt you think if i was pregnant this would happen again? Thanks for any advice or help!!