Post this along with a few pics to varanustalk.com it is a monitor lizard specific forum. You will get way more professional help there specific to your lizard.

I don't know everything about your monitor in specific. but start tong feeding him freeze/thawed mice (that have bones etc, not just pinkies!!!)

I suggest feeding a mouse or two a day and after the mice, set in a bowl of worms or tong feed them too (a little too time consuming for me tho to tong feed bugs). make sure your basking is good and hot and your humidity is high. Look into bioactive substrate too. I'm not sure about tank size... the bare minimum is 2x the lizards length is as tall or wide the tank is (depending on vertical or horizontal oriented) and the lizards length as deep and wide/tall defending on orientation.

So let's say your lizard gets 4 feet long for example. Since its vertical oriented, it would be 8 feet tall and 4 feet wide and deep.