I cut the inside of my mouth with my toothbrush last week and still hasn't healed?

Last week (maybe about 6 days ago) I was brushing my teeth as normal and I guess I went a little rough and the brush slipped from my teeth to the side of my mouth and cut it a bit but it wasn't bleeding. I just rinsed my mouth and went to bed thinking that it would heal in a day or two. And all these days have passed and it is STILL there and it hurts and stings when I eat or drink. I can't see the cut because it is on the very side and down of my mouth. Why hasn't it healed yet, its just a little cut, has it got something to do with saliva? Also should I get it checked with the doctor/dentist.