My baby is now 6+ mths old, he drools alot since he was 3.5mths old. Although we keep changing his bib every 15 to 30mins, he still got rashes on from time to time due to too many saliva on his face.
All we can do is to keep pat away his saliva with damp cotton pads and then applying moisturising cream on more often(for me almost every 2hrs), it helps to get over the rashes and prevent it to come back again.
My baby is also like that, he started drooling since 3 months old and he also has A LOT of rashes on his face since then. I tried to apply some cream but he keeps scratching his face and then suck his fingers!!! As I am afraid that he will eat the cream, I can only do it when he is sound asleep at night.