I'm thinking this may be Cocci. I have had this happen to me recently and it sounds very familar. I treated for Cocci and my bird is better now. I would try some medicated chick starter and see if it helps. But, only if the bird is still young and not over 9 months old. The medicated feed can leave a residue on the inside of the egg membrane and you do not want to eat the eggs for a couple of months from this bird. That is why the medicated chick feed has you stop by the 6th to 8th week to get it out of the system prior to the pullets laying.
Best Wishes
B
Best Wishes

B