Hi Swamperkk, and welcome to the Forum.m
I'm sorry to hear your chickens seem a bit under the weather. There are several possible reasons why this can happen, which could be dealt with before you resort to antibiotics.
First, I wonder when they were last wormed with Flubenvet? They should be done every 4-6 months, as a worm burden can pull them down and make them less able to cope with any other health problems that may come their way. You must use the proper stuff, ie Flubenvet, which is licensed for poultry and will do the job easily and effectively without any need to stop eating the eggs. See this article about worming on the main Poultrykeeper website, here
http://poultrykeeper.com/general-chickens/worming-chickens
If they've been wormed recently, could you give more details about the poorly ones? Any runny eyes or noses, diarrhoea, eggbound problems? Are their combs bright red and upright, or are they floppy and shrunken? Could they have lice, or could their coop be infested with redmite? What are you feeding them on? Could their crops be blocked with long grass, or is there a bad smell when you look in their beaks?
Of course it's not possible to give a veterinary diagnosis on here, especially without seeing the birds, but these details will help us to make suggestions. Please remember that only a vet is legally allowed to prescribe any antibiotics for chickens, and you should never ever give any antibiotics to poultry except in the most extreme circumstances. They should most definitely never be given as a pick-me-up tonic for birds. There's a thread on here about over- use of antibiotics and why we should avoid them if possible. See
http://poultrykeeperforum.com/viewtopic.php?f=7&t=8760