If i'm taking birth control pills is it possible for sperm to stay in and come out later looking like yeast?

Unlikely: Birth control pills would not change the consistency of your partner's semen, but it may change the consistency of your vaginal discharge. Some mild white vaginal discharge is considered normal. Cottage cheese-like discharge with vaginal itching might be a yeast infection. However, if your discharge becomes foul smelling, copious, or green, you should see a doctor for an evaluation.