If you are worried about your parents finding out then don't worry. They WILL find out eventually. The road you're on is a road to self destruction.
Addictions are always a manifestation of a deeper issue.
Then these pain killers become pain givers. That is why you have posted a message here to begin with. It is imperative that you find some professional help and start getting the support you need from family and friends. Addressing addiction is a very shameful duty to perform but it is also the most freeing. You will need some help in identifying the REAL issue behind your addiction.