How Does One Wean Off Speed?

I know it sounds like a dumb question but I have to know. I wonder if I’m addicted to it – I have been taking phentermine for the past couple of months and I love it. It gives me a burst of energy and gives me that feel-good feeling. I realize I could be experiencing Serotonin Syndrome. Not uncommon since I do already take an SSRI for my depression. But I fear that I’m addicted to it and when the bottle gets near empty I want to go to the doc to get more. Heck, I’ve even considered ordering online! Sheesh! What does that tell you!? Need your advice….