You may have something like an upset or a swollen tissue in the lining of your lips. It might be due to different reasons like an allergic reaction, minor trauma, or a virus infection. Typical symptoms include soreness, redness, or pressure. To reduce the pain, put a cold bandage on it and stay away from spicy foods. Sufficient hydration can also be helpful. If the issue continues or worsens, it is better to visit the doctor.