Is it normal to have yellow urine after taking multivitamins and herbal medicine with avena sativa?

Yes. Most vitamins are filtered and excreted in the urine by our kidneys. Exceptions are the fat soluable a, d, e, and k, that get stored in the liver and fat tissue. When you ingest a large amount, as is found in vitamins, you body quickly get rid of the excess in your pee. Eating a varied diet high in fruits and veggies remains the best and cheapest way to get your vitamins and nutrients.
Yes. But why bother? Multivitamins are worthless. Go exercise more.