What Could Be Brown Spot Discharged 6 Days After Period ?

I had an unusually short period this month (usually 5-6 days, this time only four days). Six days later (i.e.) today, I got brown spotting - a bit bloody. Before my period, I suspected that I was pregnant (had sore/tender breasts, mild cramping in the lower abdomen, lasting from ovulation day to second day of what I believed to be my period). I have not had any of the symptoms since my period ended (except being tired and having a slight headache, but I hit my head Tuesday so I suspect that that s why). I had sex yesterday morning and was fairly sore during, so my initial thought was that I had gotten a scratch, but there was no blood right after coitus - first this afternoon. My question is: Should I go see my doctor? I never spot between periods normally.