My boyfriends ejaculation burns me and cause me to get yeast infection why? doesnt burn when he ejaculates outside. we are wanting to have a baby

You may be hyper: sensitive to his sperm fluid, which may be a little acidic which is normal. Yeast infection typically happens when the pH environment in your vagina gets out of whack, so frequent changes in pH will encourage that to happen. And frequent exposure to foreign "substances" can do that. Also the best way to get pregnant is to chart ovulation so you maximize your chance when you ovulate.