This is not an uncommon occurance. When people do get sick, it's usually with the changing of seasons.
In these situations, often people are experiencing some sort of stuckness - how are you with adapting to life as it shows up? Do you need order and control or are you flexible? How is change for you? Are you able to easily let go, move on, adapt, and grow? In health, a person is able to move fluidly from one season to the next, from one stage of life to the next, etc.
Your Spirit interfaces directly with your body, not with your mind. Perhaps these symptoms are a teacher.
I'm not sure a Western doctor will be of much help, but of course you should be proactive in seeking medical attention. Acupuncture is a medical system that works to unite the body/mind/and spirit of a person with Nature - this sounds like a good fit for your set of circumstances. If you are fortunate enough to live in an area where you have a choice of acupuncturists, then look for a Five Element acupuncturist. The nice thing about acupuncture is that oftentimes people come in with a specific complaint, get treatment, and a lot of things resolve since it's on a body/mind/spirit level.
With any sort of phlegmatic condition, you should moderate - or eliminate - dairy, sugar, and wheat from your diet. You may be experiencing food intolerances, which often are masked as sinus issues, phlegm issues, skin issues, and headaches. Consider an elimination diet, which is a type of cleanse that gradually steps down types of food - that is if you are otherwise strong enough for a cleanse. If in doubt, a naturopath would be able to advise you.