Maybe your Vitamin D defficient and do better in the summer due to getting more vitamin D from the sun. Just today I came across a post from a doctor who said that the mother of an autistic boy noticed that her son did much better in the summer than the winter, so the doctor began supplementing Vitamin D and the boy regained full speech. Interesting. More and more research is indicating the importance of Vitamin D for the immune system. I live in warm sunny weather year round so I don't notice much difference. I think I generally do better in the summer do to less stress (kids are not in school - slower schedule). I do know that I was getting skin cancers regularly and when I stopped avoiding the sun six years ago I stopped getting skin cancers (I am careful not to get burned though). Do you supplement with cod liver oil?