Love giving BJ's but my jaw get sore

Like it gets sore just having it open at the dentist. Any suggestions (other than seeing a doctor)? Also open to tips on how to generally get better at it (hand and/or mouth stuff). I know my bf enjoys it but I want him to be shaky in the legs after, like I want him to be doin something normal during the day (like checking email or something) and suddenly remember it and then forget what he was doing