ok so where do i start?

Im a 21 year old female and i am currently on Seasonale birthcontrol meaning i only get a period once every 3 months. since this 3 month cycle began i have been really bad with takeing my pills on time, i usually take them at 9:00pm and have been forgetting to take them as late as 1-2am. at the beginning of december i started my last sheet of pills and had sex December 4-6 the same day i had sex i was put on Zithromax antibiotics for a chest infection, how ever my doctor did tell me that this could lower the effect of my BCP i thought id be fine anways and had sex twice while on a week does of antibiotics, ever since the 9th of decemeber i have had really tender heavy and sore breasts. i kno this cou;d be a sign of my period comming but i was expecting AF to come for another 2 weeks at that time. my breasts are never THAT sore that far away from my period either how likely is it that i could be pregnant? im not expecting my period till December 23rd when should i test? should i see if my period