Hello!! So Recently, Maybe Within The Last Year, Every Time

Hello!! So recently, maybe within the last year, every time I cry, about a day after I'll get a cold. And this happens EVERY TIME! Since last fall, I have been depressed, so people have told me its because of a weak immune system, but I've been eating healthy, I take vitamins. I'm a healthy person. Other then the fact in late July I was a vegan, then after two weeks became vegetarian. Not sure if that has anything to do with it, but I'm saying it anyways. PLEASE HELP ME!!