My 4 mths old baby keep yawning whenever he woke up from nap and his night sleep. Can I know why? He is breastfeed so he woke up very 1.5 hr. He does not get enough sleep?

I tbf him, he drink every 1.5hr. Sometimes 2hrly. He is a small freq drinker as he vomit occasionally. He don't have 14 hrs sleep daily. How to stretch his freq to every 2.5 hr?