Any hormonal changes can effect the amount of natural lubricants your body produces. You may have to just start using an additional lubricant or switch. I would recommend having the lump looked at because that is a pretty big size. I might be nothing more than a pimple, or cause from friction but if its a side effect of your birth control, that's definitely something to consider.
You should most Def. go to your doctor and get checked out; i've never had that happen to me so i can't speak on it. sorry