Is it possible to get pregnant three days after period leaves?

Yes: Intercourse on any day of the period can result in pregnancy.

Always possible but.: If your periods occur regularly every month then you will most likely ovulate (release an egg) a few weeks after the start of your period. So having unprotected intercourse is not the wisest thing if you don't want to get pregnant but the possibility of pregnancy is very low if your periods are regular. If your periods are irregular then you can be ovulating at any time and can get pregnant.