Refusing formula ?

My son is 9 months old, he is formula fed. The last few days I haven’t been able to get him to drink very much milk. 2 days ago he had a total of about 10oz. So just an ounce or two thru out the day from each bottle. Yesterday he had about 13oz and today so far he’s had 10oz. I can’t make him take it but I offer him it thru out the day. He eats regular food, 3 meals a deal. He usually drinks 24oz at least in 24hrs but this is day 3 of refusing formula. I also offer him water in his sippy, he will take a couple drinks and push it away. He’s not sick or anything and still acting fine/normal. Is this a phase he‘s going through? Or not normal? It’s like he doesn’t like his milk anymore, he takes a drink or two and pushes it away. I did notice he’s also got 2 more bottle teeth trying to come through but he’s not acting like he’s in pain. It just worries me that he’s going to get dehydrated!