On my left foot, i have pain underneath my big toenail. it hurts when i touch it and it is in one corner. ?

Toe pain : It sounds like an ingrown toenail. A doctor or podiatrist can help you remove it

You can do it.: Usually there are just two options. You can trim a piece of the corner out yourself, or perhaps a talented friend can do it. The second option is to have a professional treat it. Experience tells me that you might get away with trimming it yourself a couple of times, but eventually the nail will have to be seen by a specialist. Now the question is "do you feel lucky, well, do ya?".