4 month old eating every hour!?

Hey mamas! Need some ideas on this please.

This is my 2nd baby. He is 4 months old now. He was born 4.8 kgs, ate very well from day one slept very well! He is on formula.

2 weeks ago he started to wake up every hour/ every 2 hours in the night and even during the day he doesn’t drink as much milk as he is supposed to. Before he would finish a 120 ml bottle. Now he drinks 30-60 max 90 ml and more often!

Thought he would be hungry for food so started baby cereals 2 days ago but dont know what to think anymore!

Any ideas what is this?

He doesn’t seem to be in pain! He is happy...just eating small wuantities all of a sudden.

Will see my midwife Wednesday.

Thank you