His appetites changed

Daniel's appetites has changed.
He drink less milk like before.
Before he drinks 8oz every 4 hours, means 24hours he drinks 32oz.
Now, he only drinks 4oz every 4 hours, means 24hours he drinks 16oz.
What should I do?
He also eat less.
I don't want he lose his weight! I want him to gain his weight!
Oh, please god!
I'm so worry. So, so, so worry.

p/s: And, I hate dirty people to carry Daniel! Please clean urself before you carry him.