My partner and i had sex 3 days before my period. we didn't use any protection. he ejaculated and then put it back in. how likely is pregnancy?

None, if period came: If period did not come, then one can do a test. A home urine pregnancy test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred), or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test.