sniffles, planes and dogs

I'm back in Ontario this week and after a very fun weekend that included my niece's 5th birthday party at a farm (that, as a creepy side note reminded me of Babylon on Carnivale) and some bluegrass brunch on Sunday I'm in Oshawa visiting my parents getting ready for a bachelorette tonight and a wedding on Saturday.  I've planned a bit more slow time into this trip and so far it has felt a whole lot more manageable and Elliot was doing a lot better but then last night when I put him to bed he started waking up crying alot and was stuffed up. I was convinced he had picked up a cold on the plane because when we visited in August the exact same thing happened a few days into our trip but then suddenly i started to think maybe its not the plane, maybe its the places we go.  I'm not sure how long it takes for a cold to develop (do you?) but it seems just too unlucky for a healthy kid like elliot, who except for the cold he got last time hasn't even been remotely sick yet, to pick up almost the exact same symptoms again this trip -unless its not a cold and is actually allergies -to dog.
I'm devasssstated if its dog allergies. I already have the golden retriever named honey that i am going to buy elliot on his 5th birthday picked out in my head. she is a beautiful dog and she and elliot are the best of friends. if he's allergic i will be so sad. All i know is that right now he is congested but seems pretty content otherwise and the sniffles didn't start till we got to my parents house.  last time they started when we visited someone else with a dog and for the rest of the trip we were staying with people who had dogs so i just assumed it was a cold.
any thoughts?  he hasn't shown any signs of being allergic to thomas the cat and our pediatrician uses hand quotation marks when he talks about "allergies" so before i go to him for a test i need to do some research or he will just write me off as a crazy overbearing white woman.