My Mother (aged 67) Has Been Having The Problem Of

My mother (aged 67) has been having the problem of frequent urination for last 5 days (gap between two urine spells approx. 1 to 1.5 hrs. on an average). Urine Routine and Culture test is negative. No complaints of irritation or pain during urine. Complained of slight pelvic pain once or twice but nothing major. She takes medicine for Thyroid, Cholesterol, Uric Acid, High Blood Pressure. During past 2 weeks has also taken decongestant like Romilast L10, Unicarbazan Forte and Mox antibiotic tablet due to severe cough and cold. What is the reason for this sudden increase in frequency of urine passing (she had to take Urispas tablet, 1 per day during past 3 days) ?