That is the old normal range. The new range which is about 10 yrs old now, starts at 400.

You have to wait at least an hour before eating that fiberous shredded wheat. Fiber in the GI tract prevents the few micrograms of B12 from being passively absorbed.

A reading in the 400's while you are taking B12 is not a good reading. Something is wrong.
Vegans should probably take higher doses. You don't eat animal sourced foods, so you have no dietary intake at all!

Bananas are very high in serotonin. They are not allowed when people have testing for this neurotransmitter.
Try to eat a different fruit and only have bananas now and then.

Try and get more protein for breakfast. Beans and lentils are a good source and also provide magnesium.

Vegans can become low in the amino acid methionine, which is used to make SAM in the body...the mood helper. Also vegans can become low in zinc. There are supplements for both.
OptiZinc once a day or every other day is good. Will help acne if you have that BTW. Methionine is also available in capsules.