I love the advice Cassandra gave you. The only thing I can add is that my kids (and many of my friends/their children) have had a stomach bug for the last few weeks where either one has a fever, low appetite, stomach upset, diarrhea, etc. It's been different for all of us, there doesn't seem to be a "normal symptom", just a general "ick" feeling.
I agree it might be teething (all three of my children have acted like this when getting their first molars/incisors), but if it's not, try to give him things like lightly-salted crackers or things of that sort to make him thirsty so he'll take his sippy cup. Another thing I think of is, if he won't take his sippy (which he himself controls) he may be wanting comfort from having you hold his cup/straw/water bottle. From what you've said, I don't see this as a behavior for attention, but more of a "Mommy, I'm sick, I need a hug" feeling.
As far as his appetite, children will never starve themselves. My son was notorious at that age for holding food in his mouth at dinner time, just to spit it out later. It drove me NUTS! I was so worried he wasn't getting what he needed. Our pediatrician pointed out that their little tummies just aren't on our adult schedule. :) As long as he's not running a fever, and is at least getting some fluids in him, I wouldn't worry too much.
I hope he's feeling better soon! :)