I keep mine on floor lined with paper towels the first 5 days. If you already have them on shavings sometimes the shavings are too dusty and can cause respiratory problems. I took my first bag of shavings for the brooder back this month because of how dusty it was. Drafty areas are a problem too. If they are in a dusty area with bad ventilation it could be the problem. Also, soiled areas are breeding grounds for fungi like Aspergillosis (brooder pneumonia) and other bacterial manifestations. Only you know the environment in your brooder. Don't allow droppings to become too abundant and keep the water troughs clean as well as the feeders. I changed paper towels a few times a day being slow and easy about it as to not scare and stress the chicks.
Use a good quality vitamin-electrolyte in the water at 3 day intervals and add a couple drops of Poultry Rx remedy in the water trough they drink from. Keep them warm 90-95 the first week depending on where they place themselves around the brooder lamp. If you still see sneezing after a couple days, get back on here and tell us.
I've used a mixture of antibiotics for flock treatment in the past which targets CRD (Chronic Respiratory Disorder). Get a bag of Chlortetracycline and a bag of Gallimycin and mix equal parts of each together dry in a jar. Use one teaspoon of the mixture for each gallon of water and repeat for for 14 days, changing the waterers daily. Dawg54 knows of a new antibiotic besides this that works well in water, but I forget which one it is. Tylan 50 is often used for respiratory problems but is difficult to administer to chicks that young since it is an injectible.