Hello,
The biting of the top and inside of your lower lip is a good indication that either the vertical level of your lower denture teeth are to low, or set to far back from your lip allowing the lip to fall backward, as well the level of your top denture teeth may be set to low.
Can you tell me how old your dentures are and what you have, complete, partials, etc. so I can give you a more specific answer.
Thank you