Need some advice

So I got my period on November 4th and am not on any kin lad of birth control and had sex on the November 17 and and now today November 20 I have some brown discharge and this happen to me a year ago I found out I was pregnant like maybe 4 weeks like and I am pretty sure I was highly ovulating on the 17th to was not trying to get pregnant but we had a accident lol during sex