Does the pill in week 3 of the pill pack cause extremely sore breasts or could I be pregnant?

This has been going on for 4 days now and today my breasts are just now feeling ok in a bra. My period is usually a full 4-5 days with a medium to heavy flow but this past month it was about 2 days with a next to nothing flow. I started the pill pack as I normally would on that Sunday after and at the end of the 2nd week by breasts got swollen, hot and so sore that wearing a bra hurt and touching was out of the question. Im just curious what some of you might think is going on. Ive never missed one pill and everything has been normal until now.