Hi Doctor I M 25 Year Old Unmarried Female.my Periods

Hi doctor I m 25 year old unmarried female.my periods have being always be regular.only dis month I have not got my periods.itz date was 28th August n yet if has not come.I have visited a doctor n she recommended to wait for 15 days more n if it doesn't come den I can take primolut n for 5 days twice a day.she asked many questn regarding physical relatn I was nt able to ans her at her face .I have a bf bt we have never intercourse .yes oral sex was done.bt never I have taken his penis in my mouth n never allow him to put his penis inside .yet I m in fear n very worried .yesterday I did preg test using pregnancy kit .it was negative bt how much I can rely on those test.should I start those medicine? If I start those medicine n if I get periods then do I worry abt pregnancy.n evn if after taking medicine I dnt get periods den wat ll b the reason for it?.pls do reply for my every question I m worried alot.also I m suffering from psoraises and was having medicine name psorid from more den a year of 100mg which my doctor hav stopped from a mnth .could dat b a reasn of my period not cmg