What vitamin deficiencies could be hurting my weight loss efforts?

Weight loss and vits. Weight balance has more to do with what you put into yourself on the one side of the equation, and what you burn up (calories) on the other side of the equation. Vitamin deficiency or excess rarely, if ever, play a part of failed weight loss.
A Weighty Wonder. Not surprisingly, there are no known deficiency states that specifically hinder weight loss efforts. However, there are many deficiency states that acompany obesity due to poor nutritional habits that favored the development of obesity in the first place. A common deficiency is vitamin d, which is believed to play a major role in immune function, mood, cardiac health and cancer risk.
Probably not related. In america, it is unusual for a person to have significant vitamin deficiencies if he already eats an amount of food that makes him to think about needing to lose weight. This is because enriched flour, dairy products, juices, etc., are all fortified with vitamins. A person who has almost no variety in his diet may have some deficiencies, but that still should not hurt his weight loss efforts.