What Causes Lower Back Pain After Missing Dose Of Gabapentin?

I have been on 300mg gabapentin for 7 months. First for injections for lower back. Then I had back surgery had a fusion. Six weeks from surgery and doing well. But my doctor still has me taken the gabapentin to help with pain. I have noticed that when I miss a dose my pain is more intense. I am worried about what is this doing to my body.