I Am Female, Age 52. I Have Had Multiple Sclerosis

I am female, age 52. I have had multiple sclerosis since I was 39. i have trouble with urinary frequency. In the past, it was effective to avoid soda after 3:00 pm and to take a magnesium/calcium supplement morning and evening. Now, that doesn't work, and even 5 mg of oxybutnin, 4x per day, is only sporadically effective. Any suggestions?