You can get most safer sex supplies (condoms, dams, and gloves) at a pharmacy or chain store such as walmart or target. There is no age limit on purchasing them, so you should be able to get them fairly easily. For more about safer sex supplies and when to use them, check out Safe, Sound & Sexy – A Safer Sex How-To which contains information on how to put together a safer sex kit and what to do with all the supplies.
Pairing safer sex practices such as condoms with another method of birth control is your best option for reducing both your pregnancy and STD risks. There are a number of birth control options that you can use. Check out Margaret Sangers Disneyland - An easy chart of your birth control
options to see some of the various options you can try.
We recommend that people be honest with their parents; it's easier in the long run and safer for you if other people know about any medications (such as birth control pills, shots, or implants) that you might be on. If you absolutely cannot be honest with your parents, or even if you can, you can get information about safer sex, examinations,and prescriptions for hormonal birth control at Planned Parenthood at costs which vary based on income and location.
So, check out the linked articles to see our recommendations, and consider making an appointment at a Planned Parenthood to talk about your options.