It is possible to get sight bleeding even if pregnant but, it's unlikely to be as heavy or long as a normal period. The fact that you had this unprotected sex so close to a period could mean that you likely weren't ovulating at the time of the period so, pregnancy chances may be lower than earlier in the month.
However, the only real way to find out is to do a pregnancy test either at home or through your doc or pharmacy.
And, of course, it goes without saying that unless you are intending on getting pregnant, protection is the only way to ensure no pregnancy.
Best of wishes!