Low vitamin B12 can cause ringing in the ears, as well as tiredness. Also, when your B12 levels are low it's often the case that you can't sleep as well.

Many things deplete vitamin B12, particularly stress.

You might check a list of vitamin B12 symptoms and see if any others are ones you're experiencing. If they are, B12 lozenges work very well. Methylcobalamin is the form that's most nearly what our bodies use, so it does tend to work faster. Though in people as young as you, the more common cyanocobalamin seems to work fine.