Stressed and Confused

I'm on the pill and my boyfriend and I always used condoms but lately I've been worried that I might be pregnant :( I threw up last Tuesday and I've been kinda gassy but other than that I feel fine (except for stress) Today my period was supposed to start but all I've had was brown discharge. I've heard mixed things about what this means and I did only start BC about 3-4 months ago. Could brown discharge be my period?