Well, I always think consulting a vet is best. But if you can't do that, you may want to start on some Corid (amprolium) or dimethox -- it could be the beginning of coccidiosis. A vet can run a fecal sample which can pin it down better. The chick is pretty young, but if it has been exposed from the other birds, it could happen, I suppose. Usually it seems like it's closer to a couple of weeks. Cocci can kill peachicks scary fast. If you are taking it to the vet, get a fecal sample to go with you (or collect up what it deposits when you transport it -- that will be fresh...) I'm not sure if a chick that young will be passing oocysts yet -- that's a vet question, I guess.
A digital kitchen scale will usually work fine for weighing chicks, and can be had inexpensively from
Walmart or Target or any big box chain store. I think I got mine from
Amazon.
You should be able to get Corid and dimethox at
Tractor Supply or any feed store that does poultry. If you think you will need to tube feed or supplement nutrition, you can pick up some Kaytee exact baby bird food at bird type pet stores.
Double check your gamebird starter and make sure it is medicated for prevention of cocci. Some is, some isn't. I can't buy medicated gamebird starter around here (I've searched high and low), but other folks find it in their areas with no problem. Even medicated feed won't prevent all cocci in peachicks -- they are just very sensitive to cocci. But it helps. If the starter isn't medicated, you probably will need to find another way to medicate for it at a preventative level. For right now, you will want to give a higher, outbreak dose -- check @casportpony 's. thread on amprolium to get quantities to mix in the chick's water. Sometimes folks give some directly to the chick, but I am not sure how much -- Kathy can tell you better than I can about direct dosing of it.
The dimethox is an antibiotic that works against cocci -- that's sometimes needed. Supportive care is really important.
Good luck! Send a PM to Kathy if you need info on dosing and can't find it on her threads.
Oh, and welcome to the peafowl forum -- hopefully it will be on a more cheery basis soon!