Hello, although upper respiratory tract infections is one of metformin s potential side-effects, it s not a very common one in every day practice and I doubt that this was the cause of it. October to March or even later depending on the country and weather is a period during which many respiratory tract infection occur. You haven t mentioned your complete medical history and treatment, so I cannot provide more specific information. If the infections won t stop during the late spring and summer then your doctor can consider alternative treatments for your blood sugar for some time and return to metformin again in the future to check if the infections reoccur. Since metformin is essential for the treatment of type 2 diabetes, I would advise you to give it another chance. You can contact me, if you d like to ask for more details. Kind Regards!