hello, Protected sex on expected due date is very much safe and there is no chance of pregnancy. Above clinical feature is suggestive of urinary tract infection. Do a urine test for routine/ microscopy/ culture. Need proper antibiotic therapy, drink plenty water, take urine alkaliser, maintain genital hygiene properly, empty bladder in regular interval. Consult with your doctor at the earliest. In addition, take healthy diet with iron supplements, avoid stress/ anxiety, avoid salty/ spicy food stuff to get period in time. Be well & take care.