Could I be...?

Ugh Pregnant? I'm 18 years old, in school, and working. I'm on birth control but my boyfriend and I don't exactly use any other protection besides the seldom pull-out method. I take my pill every day. But I usually start my period Monday, and I started Wednesday evening. I ended Friday morning. That's a day and a half of a period (very abnormal for me). Ten days later I started discharging this like brownish nastiness. That's never happened before. I don't know what it is or why it's happening. I did some research but it didn't help too much. Could it be a sign of pregnancy or what? If anyone has had this happen and knows the answer please respond. I'm a little bit on edge about this. :/