Eye watery w/ pink discharge.

My cat Chip has been having a multitude of health problems. We just found out he has a Staph infection, might have FIP. On Thursdays he started having watery discharge from one eye, when the discharge pools on this face it's kind of pink in color. Anyone have any info or suggestions?

I should add, Saturday we started to give him his Amoxicilin and on Friday we started to give him a food suppliment (we just bought at the store) because he is not eating very much and is very, very thin. Last night I gave him his own food dish with maybe 1/2 cup of food of which he (or maybe one of the other cats) ate half of, but when I woke up there was vomit outsite his bed...

So I am guessing he vomitted. Plus last week one or two of the cats vomitted twice. It's always at night so we don't know who did it. Icarus did get into some chicken so I am guessing it was him.

So Chip is:

Very thin, like 7 lbs, and not eating much. He likes to eat when Scottie is eating, but will sit at the dish for maybe a minute then walk away.
Lethargic, it seems hard for him to really get out of bed after resting, like he is stiff.
He has his runny nose which is a Staph infection
Eye discharge,
Smells from not cleaning himself
Has bad breath from having to breath with his mouth open
His furr is always fanned out, so he of course, looks sick.

Yet, he still wants to cuddle and will sometimes want to play, chase toys we have. But only for like 5 min. then he stops.

The doctor mentioned FIP, but how can we be sure what is wrong. He has been sick since we got him, but I can tell over the past three weeks that he is getting worse. Taking him to the vet always takes a toll on him.