i have recently brought three alex, all three are almost 3months old.
among them one alex is not eating properly and he drink more water. often sleeps looking upward.
First I would have him checked out by and avian vet to be on the safe side.My female Alexandrine parakeet did the same thing with the sleeping and I believe it was due to her age (10 weeks old) and not being fully weaned. I would start hand feeding her some weaning formula for breakfast and dinner. For lunch I would hand feed him diced up fruit and veggies.