What is a reason to go to the doctor?

You can get a prego test at any drug store.

I would recommend going to the store (like walmart, or the gas station) and buy a pregnancy test there before going to the doctors. If you can't drive yet, you could walk there (just say you're going on a walk). Or even ask a friend if they can drive you or if their mom could. OR better yet, tell your mom you have to buy tampons or pads and need to go to the store (assuming she'll drive you). Then while you're there, buy a test without your mom knowing.

Another option is being honest and telling her you might need a test.

You make an appointment and go. If you are over 18, you are an adult, so the only person that needs to know why you are going to a doctor is you.

If you are a minor, it is going to depend on what your states HIPA laws are, concerning minor children and medical information, as to whether or not your parents have to be notified of any test results or medical conditions.

maybe you can say that you just go to the doctor to visit your ill friend.

Dollar store pregnancy tests are pretty accurate. They do not card you for buying one. Please don't try and steal one because you do not want to go to jail for that. Also, make sure you use protection next time so you won't have to worry about being pregnant. The weight gain might be do to stress or hormone imbalance. Good luck to you.