Hello,
Post inflammatory hypopigmentation is very difficult to treat but sometimes it goes away on its own after exposure to the sun. Creams like Elidel cream or Protropic can be used on these hypopigmented areas but at such a young age it is not advisable to use them . If the symptoms still persist then you can talk to your dermatologist about laser-assisted chemabrasion(LACA).
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.
If you've had this for 6 months and if the ENT didn't know how to fix it, it probably can't be fixed overnight. You're taking the right step by seeing a dermatologist--he/she should be able to help. In the meantime, consider using a lip balm like Chapstick when you're out. It's not super glossy, but it glistens enough that it will pick up the light and may make the coloring seem more even. Don't use it in the house, though, or all the time; otherwise, your lips will become dry. One thing you can do twice a day is exfoliate and moisturize your lips. Exfoliation sloughs off the dead cells to disclose the newer cells underneath. After you brush your teeth and rinse your toothbrush, brush your lips. They should become pinker and plumper. Pat them dry with a towel. Apply a moisturizer (not Chapstick or Vaseline because they are not moisturizers). If you don't have a moisturizer, get one in the beauty aisle in the grocery store. Do this only twice a day after you brush. Be careful not to use so much that you eat it.
Beyond that, I would recommend not letting it get you down if you can (I know this can be hard to do, and I'm not trying to minimize your feelings). But most of the men and women who are attractive are those who are who they are with no apologies. Be confident in knowing that NO ONE looks perfect--I have a friend who is a model, and she has stretch marks on her hips. Anyone worthy of you will not care if you have this flaw--especially if you've accepted it. Women find self-assuredness very attractive. If some snotty girl asks you what happened to your lip, just tell her you were in a mauled by a hamster or that some girl literally kissed your lip off. Don't apologize for it. I promise you this: No one cares more or thinks more about your lip than you do. Good luck.