Whats could be wrong thats making my period be late?

I've had my period for almost 3 years, it has been irregular since I first got it. In October it started coming every 28 days but then in May it came a week late and its scaring my boyfriend (We've never had sex, but he has fingered me) Now it's a week late again and hasn't come. It's scaring both of us, and I have no idea what to do. I can't talk to my mom about going to the gyno because I'm afraid she may think we're having sex, and we aren't. Is there any one out there that is having the same problem, or something similar? I would really like to know what could be wrong.