How likely is it that I'm pregnant?

I want to start off by saying I'm 20 years old and female, I live with my boyfriend who's 25, we're both healthy except for weak hearts and smokers [please no lectures we understand how stupid it is], the past four or five times we've had sex we haven't used a condom or tried that joke of a 'pull-out method'. I'm not on birth control and yes two of the times we did it I was either fertile or ovulating.

I'm concerned primarily because of how often we did this, I realize it was stupid and irresponsible of us and looking back now I can fully see that we are not financially or mentally ready for a child as we are both quite young ourselves.

My period is supposed to begin on Wednesday or next week and the only symptom I can think of would be odd cravings but of course that can be attributed to the start of my period since it's less than a week off.

I was wondering if there were any opinions on the likelihood that I'm pregnant? Of course I'll purchase a test if I miss it but I just wanted some fresh opinions from somebody older than myself and more experienced or knowledgable. 

                                               Thanks. =]