I Started A New Birth Control Sept 16th And I

I started a new birth control sept 16th and I ended my period the day before. I then had bleeding for 4 days starting sept. 26th. I am sexually active and have no had a lapse in taking my pill. I take it everyday at the same time. I never miss one. I recently was on antibiotics starting Saturday October 17th. Once I finished my antibiotics I start to have tenderness in my boobs and a bit of cramping. I have no other symptoms.This has been going on for 4 days now, but I still haven't gotten my period. Could I be pregnant or is it just from switching birth control pills?