Do you have any pain or "burning" on passing urine, Terminal? If so, could be a minor urinary infection. Sometimes taking "extra" vitamins can upset the balance of things. Your urine is supposed to be slightly acidic to help keep infections at bay. Some things you may take may alter this balance, and the bladder lining can become inflamed and cause you to urinate more frequently.
Also, just because you had one single test for diabetes that was negative doesn't mean you can't have it. Worth further checking.
My first suggestion would be to stop taking the vitamins, and see if it resolves. If it does, then get better advice on what vitamins and what dosage to take from a professional.
Sounds very uncomfortable and annoying.
Cheers
Mick