Re: What is this?

The bugs on the skin could be Scabies, migrating Strongyloides, or Morgellons. It's hard to diagnose from your description.

Although the nutrition problem, weightloss, and stinging anus suggest helminths are the cause. Do you have bloated feeling, abdominal pains, or eggs (strange objects) in your stool?

You could try making Papaya smoothies or eating as side dish with your meals. Fresh papaya & its seeds are potent anti-parasitics for the GI tract.