What are these symptoms a cause of? fatigue, trouble sleeping, being cold, slow digestion, headaches, bronchial/sinus infections, long term depression/anxiety, fuzzy thinking, short term memory loss, weight gain, muscle/joint pain

There : There is no short answer here. These problems are all likely not related and represent separate issues. The best advice i can give you is to visit your primary care provider for a complete history and physical. Some examples of problems you may be dealing with are: diabetes, anemia, thyroid disorder, depression, anxiety, allergies, arthritis, etc. The list could go on. All these things and more can be ruled out or in after careful evaluation. Best of luck.

Many possibilities: Dr. Jackson is correct: these may be not at all related, but clusters of symptoms from several etiologic origins. I think that depression could very reasonably be associated with a good deal of your symptomatology, with the overlaying onset of an upper respiratory infection. Firstly a thorough assessment by your pcp is in order, then consultation with a therapist to address long term depression.

Many possibilities: I would recommend you start with a good physical exam and go over all your symptoms with your doctor. Among things to rule in or out are low thyroid, and/or fibromyalgia, rheumatologist disease such as lupus, sjögrens, rheumatoid arthritis, B12 deficiency, folate (folic acid) deficiency, lyme's disease., and that just for starters. Go luck. Your doc should have no trouble figuring it out. Sleep apnea is also a possibility.