Why do I keep getting sick?

Its March and i get sick (coughing, sneezing, weak) every single week. Fist i start off with a runny nose, then i start coughing and my throat fills with mucus that i have to keep spitting out. The next day i feel the worst like vomiting and coughing makes my chest feels like there is a bomb that keeps detonating in my chest. the next day after that i feel better. this happens every single week around tuesday and wednessday. anyone know if this is a serious problem or how to stop this cycle? please tell me as much as information you can. thanks.