Wrong section po, any way No. That's a myth. The purpose of multi-vitamins such as Enervon is to prevent vitamin deficiencies thus preventing sickness.
There are some vitamins that will help you stimulate your appetite but nothing that dramatic. It's placebo effect. If I give you a salt pill and tell you your appetite will increase - your mind will believe that.
So to answer your original question, no... vitamins don't make you gain weight. Calories make you gain weight.
Instead of vitamins increase your meals nlng, check mo caloric counter online, compute ung needed na calories through BMI counter tapos try mo kumain ng mas marami. Pwede rin Protein shake pero may kamahalan.