STYLETHREAD -- LET'S TALK SHOP!

I think it's possible that you developed allergies. I know people who had no problems with allergies as children but have them as adults.
Also I think it's possible that people who grow up with animals develop an immunity but if they are away from animals for a period of time they can have an allergic reaction when they come in contact with the pet again. There is a theory called the hygiene theory which claims that allergies are more common because most people aren't coming in contact with things like tons of dust, animals, etc. growing up on a regulat basis and that children who live with pets from birth are less likely to have allergies. Anyway, my friend always had cats when he lived with his parents and was fine but now that he doesn't live with cats anymore he tends to have a mild allergic reaction when he is around them.
So it could just be that your body isn't used to the dog anymore or it could be just be the change in environment. My allergies always act up when I stay at my parents' house or my family's home in Connecticut and it takes a few days for my body to get used to the changes and they usually go away on their own.
If it seems like it's becoming a chronic problem when you go home you might want to talk to your doctor to see if you should go on medication or if you can just take something when you're at home. You can also go to an allergist and get tested so you can find out exactly what you are allergic to.

HTH!