Welcome to Neurotalk.
I don't know much about occipital neuralgia, but do know considerable amounts about Neurontin/Gabapentin, since it is used for so many nerve pain issues.
The dosage that people find effective in reducing pain vaires widely. In some spinal and peripheral neuropathy people I know, the dose has been titrated up as high as 3600mg-4800mg/day. There does seem to be a flattening curve of effectiveness, for most people; the difference noticed when one goes from , say 800 to 1600mg is greater than the difference noticed going from 1600mg to 2400mg--increasing dosages are absorbed at lower percentages.
There are side effects to be aware of--fatigue, some dizziness and ligh-headedness--similar to those of many anti-epileptic drugs, which deaden the firing rates of neurons in the spinal and peripheral nerves. These often fade with time, however. Other common side effects are water retention--since Neurontin is eliminated almost whole through the kidneys, and not broken into metabolites by the liver, one should be sure to be well-hydrated--and carb-craving weight gain.
Neurontin has a half-life of around 5-7 hours, so many people find that at whatever daily dose they take, it's often more effective broken up into three or four dosages daily rather than two.
Still, the dosages you've been on (unless your tiny) are pretty low--you might want to see if a bit of a higher dose can be tolerated, and spend a few days seeing if the side effects lessen at each level.