IS UNPROTECTED SEX GOOD
I would recommend using condom if you are gonna have sex for the first time or again......usually when you stop bleeding you are body is trying to get rid of things for 10 days after.
If you are married you can have unprotected sex all you want.....but if you are not married the risk of getting pregnant increases when not protected.
in reply to the title (i learnt this in biology in what i think the american people call 6th grade.(im British))
anyway when your have your period your body starts preparing the next egg for about 12 days. then there released from the ovary. you have the best chances of getting pregnant from days 12-16 of the menstrual cycle. then it restarts. so if you think back to when you had sex (you say 3 days) it is unlikely you have. But if your still unsure(and just in case) take a pregnancy test.