Worried!

I ended my period 4 days ago. My period was late by 3 days. Now (4 days after the end of my period) I am having brown discharge. Is this normal? Should I see a doctor? Is it implantation bleeding? I haven't had sex since the end of my period but I did have sex before my period and was really scared when it was late but it did come just 3 days late. Please help. I'm very scared.