Very often antibiotics such as cefdinir cause stomach upset with or without reflux symptoms. You may want to ask your doctor about over the counter pro-biotics. Because anti-biotics kill off bacteria they also kill off the good bacteria that our GI system uses as part of our digestion. Eating yogurt and taking pro-biotics can help restore balance to this system.
Additionally, a cold itself can cause a reflux flare. Mucous, eating differently (open mouth because we can't breathe thus sucking in more air), etc. can create more problems.
I hope you feel better soon!