4 or 5 days after unprotected sex is somewhat early, but it could be implantation bleeding if it was very light. 7 days is a long time for implantation bleeding, though.
that might be a ovulation bleed which is really rare or more commonly a break through bleed. a break through bleed happens becuz you are not ovulating so you get another period instead. i had that and my doc put me on prometrium from cycle day 14 till 28 to make me regualar again....1 month and it worked and never had to take it or have a break through bleed again. hope this helps.
love.....kimmie