I have had the exact same experience.
I used to get very very ill at least twice a year - lung congestion, coughing, stuffed head, sore throat, ending up with my losing my voice and, usually, an ear infection. i could be sick as long as two weeks during these bouts.
I also got every sniffle and cough that the kids or my hubs brought home from school (husband teaches public school) and these would last several days and make me miserable.
I can honestly say in the 3 years that I've been Paleo I have not been ill more than a single day at a time. I no longer have the big, nasty illnesses and if I DO get sick it is MILD and I'm fit the very next day. As a person who has been a "sickie" her whole life, this has been awesome and is one of the very very best things about Paleo for me. If the lifestyle did NOTHING else but make me this disease-resistant I'd still do it!
Oh, and I have suffered from bad asthma since I was a tiny child - humidifiers, drugs, had to carry an inhaler with me at all times, a few emergency room visits. Now I don't even know where my inhaler is. I have had only TWO asthma attacks since a few months into Paleo and both were mild.