What Causes A Delay In Menstruation?

hi doctor, I am 25 yers old, unmarried. I had some fun with my boyfriend 3 weeks ago, We did nt do intercourse. He did not go inside my vagina. But now a days I am missing my periods for the very first time. Please let me know, id it possible to get pregnent even if we did nt do intercourse yet. I am little scare, that m i getting pregnent. he just touch my vagina with his pennis out side only. but never went in. can i be pregnent now. If yes pls let me knwo how can i avoid the same. is there any medicine avaible to cure this. I dnt want to go for surgical things. Please help me and advice. I am located in bangalore.. Thanks pinky.