Your lizard seems to be in a slow decline. That behavior isn't normal.
It may be a parasitic problem, since its wild caught, and they all have them. A clean bill of health from the vet is always a good idea.
But because you've had it for 5 months already, I suspect your husbandry needs to be improved. I can see paper towel and big rocks in the photo. Is it being kept on that?
Please continue to search for information on how to set up your pet. That is really beyond the scope of a forum post, but you can start with the link at the bottom. Keep in mind, the person who wrote that, has had good success keeping monitors.
Another good source is the new book out on savannas called Savanna Monitors by Thakoordyal and Bennett. It is an inexpensive book, and the latest one written on captive care of monitors.
Good luck. Your pet has hung on this long, but he's a little baby, and needs you to help him pronto. Not eating is a last-ditch shout for help.
D.
Monitor FAQ