I had the same problem a week ago and started my chicks on terramycin soluble. It's 2 tsp's to one gallon of water. Take them off of any grit they are on, the meds attach to the calcium and will not work.
Also go and get some childrens liquid vitamins. I have learned to never be without them when it is cold and I have babies in my 200 year old farm house. Give them a drop or 2 daily if they are looking pretty good. Other wise, maybe one to start off with and then leave alone as handling them can cause more stress.
Good Luck
-Theresa
PS--You could take them off of the bedding you have them on, if it is shavings, but by the time you figure out that the bedding is not causing the problem, it could be too late. I would get them on anitbiotics ASAP, no matter what anyone says. I waited 2 days too long and lost 2 of my dear babies to a cold. It cleared the others up in 24 hours, but they did not start sneezing until a few days later while I was waiting to see if it was the bedding.