I believe it's just a matter of titrating up to find the correct therapeutic dose—S.O.P. for pain medications (or medications prescribed for pain off-label). Many members here have posted (complained?) that (when) gabapentin does not work for them...
...their doctors routinely tell them to increase the dose. This does work for some (like yourself) but not for others (like myself ), though it also increases adverse/side effects.

Some also find that they develop a tolerance in time, and their dosage must be increased further to acheive the same analgesic effect. However, unlike opioids, gabapentin has a dosage ceiling, above which there is no further therapeutic effect. This necessitates discontinuing gabapentin, rotating to a different medication in the same class (e.g. pregabalin, topiramate) or changing to a different class of medications.

Gabapentin (Neurontin) is probably one of the most prescribed and discussed meds on Neurotalk, so there's a lot of discussion/information in the archives.

Doc