Unlikely, but possible that you are pregnant. CheekyChops is right. The 'period' that you started on the Monday is not a real period, it's called a withdrawl bleed.
Definitely should make time to go get the morning after pill - you can get it from a high street chemist, no need to go to family planning.
Two things - why on earth would you have unprotected sex after being on antibiotics (the leaflet will tell you to use condoms for 7 days after finishing the course whether you're on your break or not)???? Your pill won't have been effective from the day that you started taking your antibiotics.
Number two - don't take antibiotics if you're not going to finish the course. It leads to antibiotic resistence and is one of the reasons that we have things like MRSA today.