What Causes Missing Periods And Stomach Pain?

hi, i am 18 and i had a intimate moment with my boy friend on 12th march, my periods cycle start on 22nd, but it is little irregular, i dont know whether my boy friends pre cum touched me or not, but i did not get my periods this month, and i am under lot of stress from past one week, and stomach is paining like anything. moreover i had some problems at home and i ate lot of tablets at once but later i vomiited some, my stomach hearts a alot. does this mean i am pregnant.