Please do not try to make important decisions while being mentally unstable. Try to sort things out: What do you really want?
Do you want to continue your relationship with your boyfriend? (And does your friend want to continue relationship although you are pregnant?) If so, it will be hardly possible for you to repent having slept with him.
Do you want to keep being a JW? Elders won't disfellowship you if they are convinced that you do repent your sin, especially if they are convinced that you were not fully responsible for your actions because of your bipolar disorder.
Do you neither want to be a JW, nor want to be disfellowshipped? Annulation of baptism may be possible if elders are convinced that you did have a sexual relationship with your boyfriend continuously in the weeks and days before AND after baptism. It may help if they are convinced that you were not fully responsible for your baptism because of your bipolar disorder. (Addendum, based on your update: There is no chance to annulate baptism if sin was not immediately before baptism, but only after baptism.)