Every time my boyfriend gives me oral i get thrush. why is this? he has no symptoms of oral thrush.

Candida colonisation: He has a fungal ( candida a.) colonization of the genital area and you have probably low immune system, or taking/inhaling steroids. Visit your doctor for an evaluation (both).

Thrush: Is caused by a fungus, usually candida. It is a normal inhabitant of skin and mouth. Even if your boyfriend does not have oral infection, he probably has a normal amount of candida. You should get tested for diabetes, a common predisposing condition to fungus infections.