Senior cat will not stop throwing up, loosing weight.

Hey guys, I'm new here and really worried about my 12 year old cat.

As a kitten he had fleas, that was many, many years ago but ever since, he has been allergic to flea bite saliva. All his life he has been getting steriod shots to keep him from itching constantly and loosing his hair. Even though he has not had fleas since he was 6 months old, he still needs the shots. He usually gets them every 6 weeks and we were told he'll always need them but they will shorten his life, yet provide a much happier one.

Anyway, it was weird... after 6-10 weeks he always needed a shot and recently he went almost a year without one and was fine. We took him in last night for one because of a "rash" on his back and he started itching. Today, he threw up 6 times, it was a liquid-yellow throw up and not a hair ball. He seems to "cry" right before it happens, I also noticed he has been steadily loosing weight and started pooping on the floor on occasion.

He is 12, 13 in March so he is a pretty old cat, but he never acted his age. He was always playful and energentic up until recently. What do you think is up? I couldn't bare to part with this cat, he is a part of the family.

If it helps, he still has a full apetite and still eats as always. Especially his favorite, cooked white chicken breast.