I suppose it could be a fueling or spark advance issue, but I wouldn't ignore the low oil pressure if I were you. Low oil pressure is NEVER good, and the fact that your engine is slowly heating up as well as using more gas just confirms in my mind that it's not getting enough oil. It could be something as simple as the oil pickup falling off the oil pump, or even accidently putting too light a weight of oil in there; but whatever the reason, ignoring the problem will only make it worse. You could go from having to pull the motor to replace the oil pickup to having to pull the motor to replace the motor. Good luck, whatever you decide to do.