Hi ryan-harris.
As John_D puts it right that every sick pigeon with some disease that commonly affect pigeons show similar symptoms as you state...
Pls talk to your vet about what he finds wrong with your bird?!?.
And pls state more symptoms like color and consistency of his droppings,eating and drinking behaviour, his breathing habits, any nasal or eye discharge, slime or whitish substance in his throat etc.
First thing to be done is isolating the bird to moniter him,not letting him make other birds sick and keep him warm and give him good easily digestable feed.