I agree that since you used protection and had a period odds are you are not pregnant. However, it is possible to bleed like a period (as heavy if not heavier) and still be pregnant. Had it my first pregnancy and it was called a subchorionic hematoma. Started bleeding about a week after my positive pregnancy test and now have a healthy daughter.
Don't worry, the normal period is the perfect negative indicator. You can't have a normal length and load of a period and keep a baby. Normal full period = no baby.
If you used a condom and had your period, you are most likely not pregnant. Some women CAN bleed during pregnancy, but if it was heavy bleeding that lasted for days you most likely have nothing to worry about.
the best way to avoid scares like this is to use birth control (patch, pill, ring, shot) AND a condom....no way is fool-proof short of abstinence, but you can be fairly sure if you're taking the pill and using a condom that there's nothing to worry about it so I would consider it :).
It is unlikely that you're pregnant since you used protection AND had your period. It would try not to worry about it, but if you are, wait a few weeks and test. I'm pretty sure you're not pregnant though.