Is it normal to be sick for some time every day

Ok so here's the story.

In 2012 I got VERY sick. I was throwing up, I had trouble breathing, severe abdominal pain, blah blah blah. I went to a lot of doctors and eventually one of them told me to stop drinking milk. I stopped drinking milk and then my illness went away.

At some point (in 2015) I became a vegan. After I became a vegan, I was full of energy.

But recently, I have been having issues. I feel sick almost every day. Here's the thing. I am not sick ALL day, just part of it. Usually it lasts about an hour, but at some point I got sick for 8 hours.

Usually when I feel sick, my symptoms are pretty mild and not digestive issues. My symptoms are usually something like coughing, sniffling, sneezing, lots of mucus, headache, sore/itchy throat, itchy eyes (REALLY ITCHY WTF), and joint pain. Occasionally I have chest pain as well.

So what happens is I feel perfectly fine most of the day, then I feel sick for like an hour, then I feel fine again and go about my day with no symptoms. It's been years since I have been sick for longer than 8 hours, but I am still worried. Why do I get colds so often and for such a short amount of time?