I have a hard red bump on my right vagina lip and it's freaking me out. It is sore and kind of yellowish. What could it be?

Several things. This could be something as minor as an infected hair follicle or pimple like lesion. It could be an ulcer from herpes or other std. It is not likely to be cancer. You should see your doctor to determine what it is and what if any treatment is needed.