(Mods, please feel free to move post if I have posted it in the wrong section)

Ladies, I have a question for you all and I am just after an opinion as I am going to the doctors on Friday if my AF has still not arrived, but here is the question...... I have 2 DD #1 is nearly 3 and #2 is 6 months and I am on the pill and this is my first month on it, I was on the pill for 5 days before we 'did the deed' without protection and that was on 3 days after my AF had finished......well now I am due for my AF and they have not arrived, I am currently nearly 4 days late??? I have done 2 home pregnancy tests and they have come back negative??? I have never missed a period before without being pregnant so I have no idea what is going on.....sorry just needed to get that off my chest...thanks