Since your weight may be slightly on the higher side, your periods could get more irregular and come at longer intervals of 60 to 90 days. Pregnancy can be ruled out for the time being, but the biochemical process takes at least 10 days after an unprotected exposure, before the UPT comes positive. Best is to repeat the test after another 7 days, say on 15th or 16th with an early morning sample. If still negative you could take Tab Regestrone/Primolut N 5mg thrice a day for 7 days and await periods. For the future, try to reduce weight to 72 kg and take protection if you are not planning on pregnancy.