This depends whether you get actual urine drops on your clothes or it is only something you doubt! If it is certain and you accidentally had urine fall on you, you can’t pray until you wash the affected area!
But if it is a doubt you keep on getting, after you clean yourself from using the toilet, sprinkle some water in your underwear, and whenever you get these feelings tell yourself that it is from the water you sprinkled. In sha Allah your condition will improve shortly.