HELP!!!!

I am only a teenager. I have been dating my boyfriend for over a year and we recently had sex a few weeks ago. I have been very stressed out recently and my period is a few days late. I also noticed some brown blood the past two days that was not very heavy but it seems to have died down. I have had no pregnancy symptoms at all the past few weeks and I don’t know if my period is delayed because I am stressed or expecting. Please help! What do you think is happening?