I don't know why you haven't been graded, but I would definitely remind sensei about that. Maybe you are training in a big dojo where it's difficult to keep track of studen't attendance, or maybe your sensei pays little attension to grading overall. In any case I would ask him to grade me if I'm ready. In the worst case he will say you are not ready yet.
In my case sensei told me the day I were to be graded and I felt kinda not enthusiastic about it because that means less experienced guys will now train with most experienced ones and after the test I'm not the least experienced anymore
) That sucks! I'm just an egoist, you see.