My lips are getting chapped from sucking d*ck 😭

I’ve been with my bf for 4 years. I’ve been giving him head at least once a week without issues up until now. In the past 3 months, my lips have been getting really irritated on the upper outer edges. It only happens after giving head and not every time. Like I said this has never happened to me until now. I’ve healed my lips with coconut oil and Vaseline, bc regular chapsticks do nothing for me. Any input on why this is happening all of a sudden? Been going down on my partner consistently for a while and this never has happened. Looking for prevention tips because I already have a good treatment regimen :)