Abnormal Vulva bleeding 3 days after protected intercourse?

I had sex with my boyfriend on the 2nd and it is now the 6th. Last night (3 days after sex) I felt a liquid come out of my vagina, when I checked it was a mucky red/brown coloured discharge. I have read that this could be implantation bleeding which is a sign of pregnancy but he used a condom and pulled out before he cummed. It didn't keep bleeding it was literally just the one blob but it was big enough that I felt it come out. I am really worried that I might be pregnant as although it was protected it was on my ovulation day which I didn't realise at the time. Is there any chance I'm pregnant or am I just beeing paranoid? I have only had sex 3 times so I'm still a newbie so I'm not sure if it could just be my body not being used to it. Also, I recently found out I was anaemic and started iron tablet 4 days ago - I'm not sure if this could be something to do with it. Please help, thank you x