This started as a classic post-coital lower UTI - urgency, burning at the end of urination, suprapubic pain. What worries me is the new constant right flank and waist pain: that is the pattern of the infection climbing up to the
kidney (pyelonephritis), and it can happen even before fever appears. This is not a wait-and-watch situation any more. You need urine routine plus culture and a proper course of antibiotics started today, chosen after examining you - not a single-dose over-the-counter tablet.
Next Steps
See a physician today for urine routine/microscopy, urine culture and an ultrasound KUB, and start antibiotics under supervision. Drink 3 litres of water, pass urine after intercourse. Go to the ER if fever with chills, vomiting, blood in urine or worsening flank pain begins. You can consult me on Practo or at Synergy Multispeciality Hospital, Miraj with your reports.