Please quit now. I know you don't want to hear that, but you are walking a fine line. Mentally you are already addicted, and just wait for the physical hell that will follow. I am an opiate addict, I've never even used heroin but I am completely and hopelessly addicted to pills. I started out the same way as you, just using occasionally, being careful not to binge or use multiple days in a row, keeping my tolerance low. And then all of a sudden it wasn't enough and I found myself binging every single day, spending all my money on opiates and going through miserable withdrawal symptoms every time I went more than a few hours without using. Addiction just sort of attacks without warning, and even if you're not completely there now (and you may be) I promise you will get there sooner than you think.

Get help now for your depression before it's too late. Self-medicating is an easy way out but will bite you in the *** over the long term. Talk to a therapist and find healthy coping strategies so that you don't feel like you have to rely on drugs to feel good.