I have a large lump just inside my vagina on the top wall. it is not painful at all and does not seem to need to be popped. could it be cancer?

Hard to tell: Difficult to tell without a pelvic exam or ultrasound just exactily what this might be. Could be a cyst just under the wall which can be left alone or drained depending on size and how much it bothers you. Also depends on if this has been there for some time or more of a recent development. If you have had pelvic exams before and was present I would think would have been noticed.