Is there another alternative natural medication to replace gabapentine?

Basically, no. Gabapentin (US spelling) is an anticonvulsant/pain drug with specific and relatively benign properties. It appears you are using it for a pain syndrome. Pain may respond to many types of treatment, depending upon the person and the condition. You might find something else outside allopathic medicine that works as well for you, for your condition. An alternative for you, maybe not for others.