My partner and i had unprotected sex 3 times in a row with 30min difference and i used the withdrawal.she is inovulating period how can we avoid preg?

Use reliable method: The failure rate of withdrawal for prevention of pregnancy is about 27%. The best way to prevent pregnancy is to use some form of birth control. She should discuss her options with her doctor.

Stop : having unprotected sex is the real answer. One or both of you should be able to say 'no, this might cause a pregnancy' and then either at least use a condom, or get her on OCP. The pullout method is the worst form of birth control there is.