tube like vaginal sore

Hi, Im hoping someone can help me. Ive recently noticed that I have a tube like lump on my labia. Ive been trying to find out what it is by looking online but all I seem to find are lumps and mine is like swollen but goes inwards kind of like a tube, its really tender to touch and is uncomfortable. the skin around it seems to all go in and it looks white inside I dont think its an STI as Ive had few sexual partners and am alwasys careful also ive recently been tested for all the routine STI's and tested negative. I dont really feel comfortable visiting a doctor and was wondering if anyone else had experonced anything simular or knew what it could be :s Thank you