Chronic colds and ear infections are the result of allergies and lack of digestive bacteria.
1. Your son is probably drinking a formula that is making him sick. Most formulas contain common allergens: corn (corn syrup), milk or soy.
Start by finding a NON-corn syrup based formula (you will find these in the health food stores or health food sections of your grocery) and switch from milk to soy. If he is getting soy already, you won't want to switch to milk as it is heavily mucus-producing and won't help, so stick with the soy for now.
2. Formula doesn't contain the good bacteria that is found in breast milk. Once a child starts bottle feeding, he will need to have this good bacteria supplemented for him.
Acidophilus is sold at all health and natural food stores. It is available in powder form. Put 1/4 teaspoon in his bottle before bed and in the morning until he stops taking the bottle.
Because he is so sick and has been for so long, you will need to continue the Acidophilus as he grows up (there is no harm here) now and then for a month at a time. It is available in chewable form as well for kids and adults.
Most children in our culture don't have good bacteria production in their colons. I was told by a naturepath that each generation of bottle fed babies removes the genetic ability to produce them. He said it is estimated to take 3 generations of breast fed babies to reset the production.
In the meantime, poor bacteria count in the colon produces allergies like your son's. Both of my kids, although breast fed, have the same problem. As long as I keep them on acidphilus and away from excessive dairy and ALL corn syrup, they are fine and rarely get sick.
3. Consider taking him to a chiropractor. Subluxations in the upper spine and neck can keep the sinus's from draining. I would definitely consult a chiro soon.
Good luck ~ A.