meal replacement/supp for work

You should not replace a meal, just take a smoothie with you. Carbs (fruit), protein (yogurt + whey), fats (oils). Filled to its neck with nutrients.

 

That's because you need "food", not a replacement or a supplement

 

Well, you say you are getting tired and weak perhaps it's not enough. I usually eat every 2-3 hours, especially when I have physically demanding work to do.

 

Another thing you can try Relentless, is buy flax seeds and grind them in a coffee grinder along with the oats and then add it to the smoothie. I add that to fruit and yogurt smoothies along with whey protein and I'm not hungry for hours.