Hi Pee,
I can really understand why you are so worried about him and this is easy to say but hard to do - try not to worry unless it becomes a long-term pattern.
If Riley is not going through a growth spurt and is still in recovery and not all that active, it might be totally normal for him not to have much of an appetite.

If his stomach is feeling a bit sensitive, he might not want dairy - it is harder to digest than fruit or water, and a couple of days won't hurt him nutritionally.

If his lack of appetite extends for more than a few days you might like to pop him down to the doctor for a checkup, but in my experience with my children it has been quite common for them to go through phases of eating like birds then hitting a growth spurt and making up for it by being constantly hungry, their appetite is very firmly linked to their physical or emotional growth spurts and plateaus.

Listen to your instincts, but as long as he is drinking I wouldn't let it worry me for a few days. As Kelly said, keep an eye on his nappies.

Good luck!

Kerrie