Have you given the dewormer? The egg withdrawal is 14 days after the last worming dose (total of 24 days.) With Corid, there is no egg withdrawal, so you can eat the eggs if you haven't used the dewormer.
Corid would not hurt them at all to treat them. Dosage is 2 tsp of the liquid, or 1.5 tsp of the powder per gallon of water for 5 days, as the only source of water, and change it daily. When it is finished, give vitamins and probiotics for several days. That way, you will know it's not cocci...
How old are your chickens? You can't always see worms in the droppings, so I would worm them with Valbazen or SafeGuard goat wormer 1/2 ml orally for each chicken, and repeat in 10 days. Stop the yogurt and get some probios dispersible powder at your feed store. Yogurt can cause more...