Thank you for your question. A yeast infection in the mouth (also known as thrush) is not normally acquired through receiving oral sex, nor giving someone oral sex. Thrush can be caused by several different causes including (but not limited to) a weakened immune system, or being on antibiotics.Only a doctor or a dentist can diagnose thrush.f you have been diagnosed with thrush, you will need to ask your doctor or your dentist the possible cause. But receiving or giving oral sex is an unlikely cause of getting thrush. On a related topic, a man can sometimes get a genital yeast infection when having sex.