D.B.
It's so hard when they are little, but this is SO common! Sometimes they get the same thing back again (because they weren't really over it), sometimes they get something else (because the immune system is already suppressed from the first illness). And when a family starts passing it around, it just cycles and cycles - and you have less energy because you've come down with something too. A lot of colds settle down in the chest and result in wheezing.
Sometimes it's worse when they get to be 3, 4, 5 years old because they are less isolated - they are in more play groups or preschool classes or whatever, and exposed to more kids. Just keep letting him play in the dirt and get exposed to germs in small amounts, don't use antibacterial products (just regular hand washing with regular soap, lots of bubbles), and keep the fluids going.