The usual story here is either the DPF needs a forced regen (done by Nissan, takes a couple of hours and is so strenuous that you need an oil change afterwards) OR your DPF sensors are on the way out (this happened to me). Replacing the sensors with factory ones might leave you in the same predicament as before. Replacing them with some from auggie (a user on this forum) will likely resolve the problem as long as the DPF isn't blocked. If it IS blocked, you can either replace it ($4K from Nissan, or try one from a wrecker), hollow yours out (a 2kg hammer and a cold chisel is required, plus a box of bandaids for when you miss the chisel and get the fingers holding the chisel) or get the DPF Delete pipe.
You might also check up on the left hand guard beside the ABS unit is a small black box with two rubber hoses connected to it. These rubber hoses connect to two metal pipes that head down under the car. Those metal pipes are simply connected to the exhaust before and after the DPF. If one of the hoses has broken or come loose, the little black box - which just compares the pressure from each hose - will report to the ECU that the DPF is faulty. You might get away with it cheaply!
Good luck with it.