I am bulimic and underweight. i stopped getting a period about 8 months ago. i had sex 17 days ago. is it likely i'm pregnant?

Unlikely: both your low weight and your lack of periods strongly suggest you are not ovulating at this time. However, one can never be certain. It would be prudent to get a home pregnancy test and check and repeat the test in a week if negative. It would also be wise to use protection for unwanted pregnancies and STDs.

Not likely: Having no period for 8 months means that you haven't ovulated for 8 months. You have to ovulate to get pregnant. While you might have ovulated around the time you had sex, it's not likely. However, pregnancy is a possibility whenever a woman has unprotected sex. It's pretty unlikely for you though.