OK, so this is just a possibility, I've no idea how common this is. Poking about inside one day a couple of years ago I felt a bulge. It didn't feel like a lump in the vagina, more like something outside the vagina pushing against it and making the vagina wall bulge inwards, about the same size as my cervix, but to one side and a little lower down. It was a fibroid on the outside of the uterus on a stalk, probably been in there for a long time, but had moved, drooped down so that it was sitting against the vagina wall. Maybe just gravity, but i'm sure coughing could do the same?