How to know that the multivitamins iam taking actually helping me or making any difference?

You often never do. Unless you have a lab proven vitamin deficiency that improves on tests, you may never be aware of the difference. Vitamins are co-factors in our bodies metabolism that improve efficiency. Those on a broadly inclusive diet may already get what they need without vitamins, so supplement would just be flushed from the body daily.

It has to do with the context in which the vitamins are taken. If replacing for known deficiencies, improvement in symptoms with levels being checked would provide required information, if taken empirically in order to help with specific symptoms, improvement or lack of it would help answering your questions. Otherwise vitamins are not recommended for patients having a regular diet.

If you are eating a mixed diet, you do not need supplemental vitamins. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV, Flu and Covid vaccines. Wish you good health!