Why do I always get sick in the fall?

Okay so I've noticed over the years that whenever fall time comes around I'm either experiencing a bad infection (like ear infections for example that's only happened once) or I'm experiencing a intense sickness like tonsillitis. (Which happened to me last fall) or if it's not anything intense like that then I'm very sensitive to dairy products. I've always been a bit lactose intolerant, but I've mostly just been careful with how much dairy I had and too much would give me a problem... but especially this fall season I've been REALLY sick from it. The smallest amount of dairy will make me throw up, just by having ranch dressing to dip chicken into made me throw up the next morning with the worst stomach ache I've ever had, felt like my insides were being ripped apart. Idk how to explain it but it was painful.... anyways, I've had times where dairy made me sick alot but never this badly. I'm just wondering if it actually has something to do with the season and if there is anything I can do or anything I can take, like if there is a certain vitamin or something I need. Just need to know if this is a normal thing for some people and if it can be prevented in the future.. just all in all I need to know what to do.... or if I do nothing and accept that this is my life lol