Neurontin isn't a 'quick fix'. It has to be in the body at a specific level 24/7.
900mgday is just a starter dose to start to build it up in your system.
I woudn't think you'd feel anything significant.
Usually it can take 2-4 weeks before any difference is felt.
Considering that I was taking 4,200 mgs/day before I switched to Lyrica,
your dosage is a significantly small one.
Most don't feel any results until at least 1800-2400mgs/day and it would be advisable to also take a pain med along with the neurontin. Most of us use a 'cocktail' of two or more meds together with neurontin for best results. I take Tramadol (Ultram) 300-400mgs/day.
Neurontin has to be taken in regular, equally divided, doses- so that a level amount is continually in the bloodstream 24/7.
It really isn't designed to be taken as an 'as needed' med.
(I am not saying that is what you are doing-I am just stating its usage)