I'm 15, had unprotected sex, and have been getting a lot of tummy ache

You are right to say that you can still get pregnant very easily with the pullout method, as there is leakage of semen before the final ejaculation. The first thing you need to do is have a pregnancy test. You can have this done for you with a simple urine test at a pregnancy centre, a young people's clinic, or many pharmacies offer the service. If you want to do the test yourself, you can buy pregnancy tests quite cheaply now from a local pharmacy or beauty store. If the pain is constant and getting worse, you should see your GP immediately. I would also recommend that you have tests for sexually transmitted infections, as these are passed on by unprotected sex. You can go to a walk-in GUM clinic for these checks. If you need more help or information, please have a look for your nearest pregnancy choices centre and get in contact with them. You can also follow this link for more info about pregnancy tests.