What Are The Side Effects Of Alesse Birth Control?

I began on birth control using Alesse last month, and got my period during the placebo pills, but switched to Yasmin the following month, and am currently about half way through my pack and experiencing, brown bloody spotting and discharge, i have been experiencing this for about a week. I had unprotected sex, the 4th day using Yasmin, but boyfriend with-drawled way before coming. I am wondering, what this spotting most likely means, could I be pregnant? or is this breakthrough bleeding? I'm also experiencing tender swollen breasts.

Thank you!