Oh, poor guy. He has really had a tough time lately.
I'm concerned with the odor as well.
The desciption of a metallic smell makes me think that he could have an anal gland impaction or infection. The anal glands are located just inside the anus. It is a common source of odor to this area. If there is an infection, or the glands are full and small amounts are leaking, it can cause the odor, plus the licking and scooting.
In addition, anal itchiness can be caused by intestinal parasites and food allergies.
I would recommend a repeat veterinary visit to have the anal glands checked and emptied, even if they were emptied a couple of weeks ago - they can fill quickly. The glands may need to be infused with an antibiotic/steroid combo if they are infected or inflamed.
In addition, you could take a fresh stool sample with you for a fecal floatation check. Many eggs
and some parasites are microscopic, and need microscopic evaluation to detect.
Finally, if the glands are normal and the fecal check is negative, he may need medication to decrease the anal itchiness and treat any secondary infections. Please make sure your vet does a thorough rectal exam to look for strictures, hernias
, and fistula formations, as well as polyps (even in a young dog).
food trial will be needed if symptoms persist.
Fistulas (more common in males - could be developing but not all the way through to the outside yet):
I hope this information helps, and that he has relief soon. Please let me know how else I can help.