Frequent urination can be a symptom of diabetes but it isn't necessarily a symptom of 'early' diabetes. Indeed many T2s are diagnosed with no symptoms and are quite shocked when a blood test shows their levels to be diabetic.
When the amount of glucose in the blood has become higher than what's called the renal threshold , the body wants to try to get rid of it. That threshold level is normally a blood glucose above 10mmol/l, and if you had glucose levels consistently above this (enough to cause symptoms) then it would show up on a urine test. In T1 the levels pre diagnosis are in fact usually much higher than this and the body may also be trying to remove ketones (caused by the breakdown of fat) into the urine. Ketones can also be detected with a urine test. It is consistently high levels that cause frequent urination.
Because of the water loss , the person becomes dehydrated so is also really, really thirsty, drinking a lot more to compensate for the water loss. Personally, I don't normally drink a lot but drank huge amounts. My urinary output prior to diagnosis was high in volume and almost colourless.
Your urine tests and blood tests were negative. Go back to your doctor because you're obviously concerned and ask him to discuss other possible reasons for the frequent urination.