Shandi,
it will be okay. There are many options for you. You can just simply tell your mom that you are not feeling well, aren't sure why, and would like to go see a doctor. I am sure that she would rather have you tell her than go on feeling the way you do. You don't need to necessarily mention anything about pregnancy. Patient confidentiality is key in health care situations. You can talk to your doctor about anything you like and he will not relay any information to your mom. You can also go the store and get a home pregnancy test yourself. You can also go to a nearby clinic such as planned parenthood and see a doctor there yourself. You do not need insurance and the cost is fairly low. It may not even be pregnancy. Women usually don't show signs of pregnancy until a couple of months after conception. Many things can affect women's periods such as stress, diet, exercise, etc. Just try to relax and your body will adjust.
Hope this helped. Best of luck.
Natalie

Sweetie take a test... Talk to someone whos close to you....

You can go to your local health department or planned parent-hood and get a free test with out parental consent. They don't have to be there, or know about it. That way you know before you drop a bomb like that on your mother