Can I know why my 4 mths old baby keep yawning? He will always wake up 30min duration for his nap himself without being disturbed. Not enough sleep?

Yawning is a sign of insufficient res. Baby may be experiencing sleep regression so they might wake up when they transit from 1 phase to another (light sleep and deep sleep). We were on standby to tap or rock him at night but good thing it was ok in the day. Allow baby to suckle thumb or use pacifier to smooth themselves back to sleep - or other soothers that they use usually. It's a phase ad they will get over it with your help for now