Optic neuritis can come from very low B12 levels. I suggest you get this tested. You should be at 400pg/ml as the lowest new normal. (doctors will call 200 "normal" so you have to be proactive and get the numbers).

Also since you are YOUNG, you may have the DNA mutation called MTHFR... which prevents cobalamin and folic acid from being activated to their active methyl forms. A test for this is not that expensive and may reveal much that would help you thru your coming life.
This mutation is common, and will lead to elevated homocysteine levels over time, and heart attacks/strokes in the future)

There is a rare form of optic neuritis that is made worse with cyanocobalamin (the common synthetic form of cobalamin in many vitamins). If you have this you have to AVOID cyano form always, and only use the activated types. (hydroxocobalamin, or methylcobalamin).