How do prenatal pills affect my attitude and weight?

Vitamins. Most people don't find a problem with weight gain on prenatal vitamins. Attitude is a difficult answer as this really depends on your attitude toward being or getting pregnant. The more common problem is constipation which can be helped with increased fluids, fiber or stool softeners.
Positively. Prenatal vitamins should not have any adverse effects on you, and may make you feel better, even if you are not yet pregnant.