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Unprotected intercourse can always lead to pregnancy and chances are more during the ovulation period.If your periods have been regular and you have missed them now then possibility of pregnancy can be suspected.
Urine test is not reliable as it is callibrated one and can take 10 to 12 days after a missed period to give results.Drugs might delay the period for few days but not longer.
Get a Blood HCG test done for pregnancy determination as it is confirmatory test.
Some other causes can be hormonal imbalance which can be due to some issues as ovarian cysts,endometritis,pelvic infection,stress,thyroid disorder etc.
Kindly visit a Gynaecologist for detailed evaluation.Have healthy balanced diet.Restrict smoking and avoid stress.
Take care!