What to do if i take 1200 mg of gabapentin twice daily and still have back pain. how much more can i take?

Pretty high dose: If your current dosing regimen isn't relieving your pain, you should bring this to the attention of the prescribing physician, who may recommend alternative medications.

Gabapentin dosage: You are not at the maximum dosage for gabapentin. If you don't have good relief from the medication, you should discuss with your doctor to increase the dosage or have it changed to another medication like Lyrica (pregabalin) or gralise.