Hey man
It seems like you answered your own question in your post. You are not eating enough. Look at the stickys set up in the dieting section there you will find a lot off info. Basically 6 meals a day, all six with protein, if you are not hitting that protein mark, you will not grow, multi vits does not make you grow.
It is like building a house, multi vit is maybe the skill of the builders, but protein is your bricks I would say.
Start breakfast of with a shake or eggs, like 6 to 9 and normal oats, not oatso easy alone. Further more you can do more shakes during the day if it is that difficult to eat correctly with your work. Shakes is not the best but in some cases it is the only solution. You can add biltong and nuts as well to eat on the go. Take your food with you, if there is a will there is a way. At the moment I am staying in a guest house and my diet is still not that bad.
Add glucose/dextrose to your post workout shake as well.
Read those stickies, knowledge is power. (or size hehe!)
"I want to fulfill my potential. It's as simple and as difficult as that." - Evan Centopani
'every chef is not a bodybuilder, but every bodybuilder is a chef'