What Causes Delayed Periods?

i havnt had my period since dec 27. i have been with my bf for a few months now and we have protected sex. does that mean i am pregnant. ive had all the symptoms for when i get my period but havnt gotten anything. i already have a 2 year old and i dont feel any symptoms of pregancy either. but my bf's mother said that maybe my body is changing and that is normal. is she right? please help me out if you can. i dont have insurance so i have to pay out of pocket. would it be best just to go to the doctor.