Things to try:

1) If you are low in B12, then you are not making melatonin from serotonin. No melatonin = no or poor sleep
So you can get tested to see what your B12 levels are.
Or you can decide to take it anyway.
1mg (1000mcg) of methylcobalamin daily on an empty stomach may improve sleep

2) people vary in responses to amino acids taken separately.
You can try taking the tryptophan every other day, or every 3 rd day etc to mimic natural ingestion from foods.
Genetically there are amino acid disorders, but they are not common. Stimulating the synthesis of serotonin is helpful to a point, but there is always the chance of causing a surplus.

Unfortunately we do not have a window or dipstick to measure people to see exactly what each needs. When you are doing something like this and run into side effects, then you have to step back and see what changes you may need to make in what you are taking.

Is tryptophan the ONLY thing you supplement with? Do you take other drugs for other things?

Remember, the goal of using supplements wisely is to restore a balance that is skewed.
They are not like DRUGS, which create effects of their own.