Girls, what analysis should I have done to find out which vitamins my …

Girls, what analysis should I have done to find out which vitamins my body needs. That is, deficiency. Just wanted to buy vitamins after the results of the tests. Our treating doctor only took hemoglobin and says that now all children lack vitamins and prescribed iron and multivitamin without any test results. And I still want to know exactly what's missing from my body. I would like to go to a private clinic. I googled it, it turned out that an electrolyte test is correct?