It is unlikely but still possible. Every woman is different, and if you don't want to get pregnant, then you should use protection all the time, even during.your period. Not only to protect you from getting pregnant, but to protect from stds as well. If you're experiencing any symptoms of pregnancy, then you should see your doctor.

Yes, while not as likely it is possible, any time you have sex, you can become pregnant, even with a condom ( they are not 100 percent)

Is this three days after your period started or ended? If after it started, odds are quite low... if after it ended, odds have increased.

As beachloverjohn and Fr_Chuck said, pregnancy is always possible. Use protection every time; no exceptions, if you want to lessen the odds of pregnancy.

Now you will have to see what happens when your next period is due.