What Causes Frequent Urination During Nights Along With Difficulty In Emptying The Bladder?

I am on Toleraid tablet for my bladder I haven t been able to empty the bladder properly and I catherterise myself first thing in the morning and at night before going to bed. Just recently I have been getting up through the night 3 to 4 times a night instead of 1 - 2 times what could be causing this.