Gabapentin is a firstline treatment for PN, despite studies that claim it only works for a minority (~1/3) of patients. Many think Lyrica works better, but since Lyrica is still under patent (and hence more expensive), the less expensive gabapentin is often/usually tried first.

Weight gain due to increased appetite is a common side effect of gabapentin. This may or may not lessen with time; there is no way to predict, as everyone responds differently. If you find any side effects to be intolerable, IMO, you should contact your doctor to discuss a possible change in dosage or medication.

Doctors prescribe dosages based on information provided by drug companies, studies, and their own experience treating patients. Still, they may not be appropriate for every patient. In my own & wife's experiences with gabapentin, and those of some others I have met, I personally believe that the recommended dosage may be more than needed for some people. Some patients may be able to benefit from much lower than recommended dosages. If the gabapentin is controlling your pain at a lower dosage, I would talk to your doctor about using, or reducing to, that lower dosage and forgoing any further increases unless/until needed. This is something that needs to be discussed between individual doctors and patients (we're all just peers on the internet).

Doc