First of all, smoking and chewing, biting or pricking the skin of the lips should be avoided. The most effective solution for treating dark lips is alexandrite and ND-Yag Q-Switched laser treatment. Please discuss these options with your dermatologist.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.