XP: 3 month - feeding question again??

FTM115

So my 3 month old DS has gone from drinking 4 oz. bottles every 3 hours during the day to barely finishing 3 oz. every 3.5-4 hours. He finishes first 2 oz. in like 5 minutes and then just plays around with the bottle for over an hour. I have tried changing the nipple to level 2 but same thing. What is going on, anyone experiencing this?

He was drinking around 24 to 27 oz. in 24 hour period before. Is that enough? If this keeps up, he'll barely get 20 oz. He has enough wet and poopy diapers so not sure if I should worry. Is this just a phase? Any feedback would be great.

 Thanks a lot.

Edited the age, he is 3 months not 3 weeks.