This could a allergic reaction to something.and a lot of it depends on how long have you had it. Dos it gos down.dos it return again. If it hurts. It mite even be some kind of infection you have..I think you should really see a dr for it. So you can find out what this is.. Good luck.
I am not sure about dry mouth but may help you out with your swollen inner bottom lip. When you put in your lower dentures try lifting your tongue up as far as possible. I believe what is happening is that a small part of your tongue is somewhat caught. Give this a try it should really help you out.