Hi, I am 17 and have been with my boyfriend for nearly 4 months. I have been on the pill for about 10 months and we usually use condoms as well when we have sex. I finished my period and took my pill, as usual, on Saturday. We had sex this same day but half way through the condom came off but we carried on anyway. Since this I have been urinating a lot more regularly and today, on the Wednesday, I have been experiencing headaches, been extremely tired, have vomited once and feel a little faint when I get out of bed. My next period isn t for another 16 days but is there a chance that I could be pregnant? Does the pill work on day one of using it?