If you have a sore at the corner of your lips despite using Blistex, it may be beneficial to show it to a pharmacist or a nurse at the pharmacy. There could be various reasons for the wound, such as dryness, ulcers, or cold sores. If it is just dryness, you could try using a lip balm like cicaplast, which is a moisturizing and repairing balm. If the issue persists, it would be best to seek further advice from a healthcare professional.