My Mother In Law Is Ninety Years Old.she Was Prescribed

my mother in law is ninety years old.she was prescribed this medication for frequent urination.IT IS 800/162 mg 2 times daily.she has been seeing bugs all over everywhere.the dr. is on vacation .she was told to take this for 3 day's for her urination problem is this a side effect for this medication.please advise
the name of the medication is soulfame/th/trime thoprim 2 daily .he gave her a 3 day supply.we ARE VERY CONCERNED