hi i am 20 years old . i had sex with my boy friend. and for past 6 months i have not keep sex with my boy friend. now my parents are taking me to doctor to check up .will doctor find out that i had sex with my boy friend.

Not if you don't tell the doctor. BUT, and this is a big BUT if you don't tell him and you contracted an STD he does not test for, it COULD cause you to be sterile later in life OR, in some cases cause permanent brain damage leading to dementia.

hi i am 20 years old . i had sex with my boy friend. and for past 6 months i have not keep sex with my boy friend. now my parents are taking me to doctor to check up .will doctor find out that i had sex with my boy friend.
no way would a doctor no just chill doctors may be clever they are not mind readers

Ok, I'll play along... you're 20... (kinda weird your parents are taking you to the doctor when you are an adult, but whatever)

As has been said, the doctor will not know you've had sex, but it is important to tell him/her. Be an adult and tell the truth; it can have negative effects on your health if you don't. Besides, since you are 20, your mom and or dad won't be in the room with you, and your doctor cannot tell anyone what you discuss with him/her.