What Causes Brown Vaginal Discharge While On Birth Control Pills?

Hello i have a question. ive been on seasonqiue now for about 6 years or so and i am 25 years old. I got my period on the 14th and it ended the 20th. I started the new 3 months supply of pills on the 17th and on the 22nd i had sex with my boyfriend. we do not have sex often at all because we are always so tired. So on the 26th i went to the bathroom and noticed i had brown discharge in my underwear. I put a tampon in and by the end of the night there was nothing. I woke up on the 27th and i went to whip and there was more discharge (brown) and then once again put a tampon in. Thoughout the dark the brown dishcarge got lighter and then a little bit of blood showed up and now its likes a dark deep brownish red color and it looks like a dark period. Can this happen a week after i just got it on the pill. I have been super stressed about work and what not, and now i am scared.

I did make a doctors appointment for tomorrow but i just want to know what this could be. I am so nervous and making my self sick over it.