I Am 67 Years Old, Strong And In Good Health

I am 67 years old, strong and in good health except that I have diabetes type 2. For a couple of years, I've been experiencing muscle weakness, dizziness, pressure on head and shoulders, pressure in abdomen. It has become debilitating. Often my hearing goes out until I sit down. Also sometimes my eyesight goes white. Sitting usually immediately stops the symptoms. I have been to a number of doctors, looked for medication side effects, etc. to no effect. I can now barely walk across the room without my legs and arms feeling like they weigh a ton. Pressure on my head, shoulders and back of neck. I have lots of energy, eat a healthy diet, do not smoke or drink. Any thoughts?