I have 3 cats that just got over an eye infection that were treated with an antibiotics from my vet recently. ?

Now I noticed that all 3 of my cats are sneezing and sniffling big time as if they all 3 have big colds. They are all still eating real good and eating really good though. Is there anything I can give them that is over the counter that will help them or do I have to see the vet again? I wonder if they picked up something while I had them at the vet a couple of weeks ago while having them treated for their eye infection? Go figure? All 3 of my cats are 100% indoor cats. I don't want to see this turn in something worse for them. I do have a steamer that I can take in to the bathroom and sit in there with them a few times a day to keep the phlegm loose so it wont get tight in there nose and chest. Any advise would be greatly appreciated. Just trying to keep from having to spend any more money if I don't have to is all. If I have to I don't mind but if I can do anything to kelp them get any better by helping them with giving them anything that I can buy from the store? Please let me know. That would really help me out being I have a total of 9 animals and that would really help me out but like I said... I will if I have to take them in. I am a responsible pet owner and will do anything to help my fur babies when they do need medical attention. Thanks for any advise friends. Cath :o)