5 month old baby has hives with cold...please help.?

I have a 5 month old daughter who has a congested nose and cough. No fever. Well starting yesterday afternoon she started with these hives. They began on her chest and got on her arms. I took her to the doctor this morning and he wasn't 100 % sure what they were. He said sometimes there just part of the virus she has. But I thought when you had a virus you had a fever or other symptoms but she doesn't. It's just congestion in her nose and a cough. He said as long as she didn't have a fever or wheezing (which she doesn't) she should be OK. While we were in the doctor's office, hives popped up all over her face, and as soon as I got done feeding her, they were gone. She had her hands on her face while I was feeding her (she always does that) and then the hives were all over her face. So I told my mom who was with me at the time to run and get a nurse. The nurse came in and I showed her the hives. She said it looks as if she's allergic to something that's getting on her skin, I tried to explain to her that we haven't switched up anything, the only thing we have given her that's different was Vick's Babyrub for her congestion and she said she highly doubted that was it...but that's the only thing. Before we left the doctor's the hives on her face already went away. That's how quick they came and left. If you could just please help. The doctor's didn't seem to worry, they checked her lungs and everything and said she was fine, said her ears, breathing, and throat looked good. They said she didn't have a fever, so that's a good sign...i just need answer's b/c these hives are scaring my husband and I. Thanks so much for all answers!