Hello Doc....I Had Sex During My Ovulation Day I.e. On

Hello doc....I had sex during my ovulation day i.e. on 24th of earlier month which was the is 14th day in my period cycle and after that I was suppose to get my periods on 12th or 13th dates but I didn't had it and I am delayed by 18 days ...what Shud I do....I haven't tested it yet coz m scared of it.... please suggest me some medicine to start my periods and avoid pregnancy.