Dear Z.,
I like your subject name, "cold rotations". That is and isn't what is happening. This is how I understand the "rotation", or cycle:
We all know "cold" symptoms: sore throat followed by runny nose, sneezing, coughing, might be some general lethargy, might be some runny eyes, kids may have a little temperature. These are symptoms of inflamed mucous membranes. The linings inside your nose and your mouth are mucous membranes. A "cold" is any one of several hundred different viruses that attack and cause these mucous membranes of your upper respiratory system to get inflamed. (Your lungs are your lower respiratory system.)
By contrast, environmental allergies are caused by pollens, dust mites, molds, mildews and their spores, and other microscopic things that might be in the air. They are breathed into your body through your nose and mouth. If you develop inflammation to your mucous membranes from them, that is referred to as "allergies" or "hayfever".
Allergies present in many different forms. Most of us are allergic to poison ivy, for instance, and develop a terrible "contact dermatitis", a rash, from it. Some people have life-threatening responses to antibiotics or bees.
One inflammation can pave the path to other sensitivities. I think of it as; if your defenses are down, other problems can show up that wouldn't normally persist.
So, you get a cold. The virus comes and goes. But meanwhile, there are new pollens in the air - hayfever season hits. The mucous membranes are already a bit irritated, so they stay irritated and the symptoms persist because of the hayfever. The catch is, that with the irritation persisting, the mucous membranes are more prone to picking up the next viruses or bacteria that they are exposed to.
With any sort of tissue damage, there is swelling and irritation from something that is released caused "histamine". So, colds and allergies will both cause "histamine reactions".
"Antihistamines" fight the symptoms of both colds and allergies. Claritin has replaced Benadryl as the antihistamine of choice for allergies because it usually doesn't make people tired.
Sudafed is a stimulant that kinda shrinks the mucous membrane's swelling.
Just on the side, I read that with global warming, our local plant growths are changing slightly. This means that plant pollens that your body adjusted to 20 years ago may have changed.
Sometimes, the back of your nose will run and not the front of your nose. This is called, "post-nasal drip". The mucous continuously sliding down the back of your throat can cause anything from a frequent need to clear your throat, to sore throats, to coughs. The cough occurs when it slides down the throat into the lungs. Then the cough reflex kicks the guck up and out.
If you reduce the mucous production, there is less likelihood that old mucous can go into your children's eustachian tubes - from their throats to their ears, causing increased pressure and possibly ear infections.
I don't know if I've made anything clearer with my explanation, but the bottom line is, keep your son on the Claritin to reduce the swelling in your son's mucous membranes.
Good luck!