should this be pregnancy?

hi im RR 21..im having sexual intercourse with my boyfriend for more than a year..usually my period is inconsistent in date..for example ill have my period at 14th then the other month it's in the 25th..we use withdrawal method properly.. ever since there is no ejaculation occurred inside,when my boyfriend feels that it is coming he will immediately removed his penis and he will have to masturbate it first before his ejaculation,it would take a minute to be on that..now my menstruation was delayed again,it should come on march 25th but 'til now it wasn't coming..and i rem.i was drinking for almost everyday last month and this month,stressed,late sleep and eating sour foods..what do you think is my case?am i pregnant???im paranoid.. ;{
response asap please..