If there were cracks or breaks in your lips, then that is how bacteria like staph and candida would enter. Staph and candida are very common in the environment and even healthy people can live with these bacteria on their skin - its only when the skin is broken that they have a chance to enter and cause damage.

As a result of the infection, your lips become inflamed. Inflammation is the body's natural response mechanism as it tries to fight the infection. The crusts on your lips are forming because due to the inflammatory response your skin cells in the lips are producing skin at an abnormal rate.

The problem with EC is that even if you get rid of the infection, the inflammation can continue because it has become chronic and the cells still 'think' they need to be producing skin at an abnormal rate.

My advice is to first treat the infection aggressively and then treat the inflammation - steriods won't work but you could try UVB light therapy as detailed in this study: http://www.ijwdonline.org/article/S2352-6475(15)00017-9/abstract?cc=y=

So there you are then.You say you get stressed at school and prolonged stress will heighten anxiety and nervousness. I was a very nervous kid myself and one byproduct of this is that you internalise a lot of what is going on, lip picking/biting is a byproduct of this internalisation. School is a tiny part of life, in fact it's not all that important at all. Try to take time for yourself, relax more, try to figure out what it is that is stressing you out so much and take steps to address this. A good step to take would be to eliminate refined sugars in processed/junk foods, and try to increase your intake of fruit and vegetables.

It sounds as though you have the beginning stages of exfoliative chelitits, make sure not to peel ot bite them from now on. If you must, purchase some aquaphor and keep the lips constantly moistened, see daniel miller's blog.

Tricyclic antidepressants block out more signals than brain signals like allergic reactions. In the past, I wrote a post about this to see what the connection was to EC lips healed with tricyclic antidepressants, which are outdated antidepressants not prescribed as much today because there are more side effects due to all the processes it affects.