I started taking Metformin XR 1000 just over 3 weeks ago as an adjunct to insulin (Novorapid and Lantus). I have noticed a "thick head" ... not quite a headache but also feeling not unlike a sinus infection and tinnitus. I put these symptoms down to having come off of a lingering URTI ( nearly 3 weeks) but not convinced that is the cause. I am 72 yrs old and keep myself fit by 5-6 days a week at the gym and in addition walking every day. Can you comment please ?