I think it's fantastic that you are improving but I think the vitamin are a placebo. I think your progress is from leaving them alone + applying moisturiser 3 times a day. Stress and lack of nutrition could be how the lips became chapped, but the exfoliation you describe created a deeper scab/wound and more inflammation.
Do you get the white line/gunk build up after sleep ? I still get this, sometimes my lips are stuck together in the morning and I'm not quite sure how to manage this aspect of it.