Can severe tooth decay cause frequent urination/incontinence along with pain throughout the body?

More info needed. Age of patient? Medical history? Medications being taken? Infection from decayed teeth? Tooth decay itself will not result in incontinence. Systemic infections can have serious consequences, however. It's time to restore those teeth and see a physician for a complete physical. All the best...
Possibly. If you have a severe untreated infection that is spreading to other organ systems, then yes this is possible. However these may be coincidental but unrelated problems. You need 1)Immediate Dental care to eliminate the infection, and 2) Immediate evaluation by your General Physician with possibility of specialty referral. Please don't put this off.