I had unprotected anal sex today after taking Misoprostol on Tuesday. Will I get an infection& is it ok to take plan b after the medical abortion?

Birth control. Since you had an abortion this week that tells me that it is important to you not to get pregnant. Please see an Obgyn and get started on birth control. This way you can take control of your life and be pregnant when you want to be. Having anal sex a few days after a medical abortion does not lead to infection unless your male partner is carrying an STD.