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I guess you can try to rule out other things.

Optic neuritis is a sign of low B12 levels. So it would be a good idea to get tested. Get your results too, don't accept "normal" because US labs still report lows as "normal". The new normal cutoff now for the past decade is 400.
In other countries this result is reported in different units...so when you get your result bring it to me and I'll convert if necessary.

If this started AFTER the birth of a child, I'd also increase Omega-3's in the diet. Having a baby really depletes the mother of these essential fats, because they go to the fetus and its developing brain, leaving the mother short. Low Omega-3 status can affect nerves too. Fish oil, is a supplement you can use 2 or 3 a day with food, or increase fatty fish in your diet, and eat flaxoil or flaxseeds that are ground up.
Also if you are low in magnesium the blood vessels in the eye can spasm and give symptoms. Foods rich in magnesium are almonds, beans, and yogurt. Don't purchase magnesium OXIDE however, as that is not absorbed. Get a chelated type like citrate, gluconate, lactate, etc.

These are two things you can do yourself. If your B12 IS low,
I can suggest how you can fix it...you don't necessarily need injections. Oral can work well if done correctly.

After these two things, other medical testing can be done.