Yesterday night, I figured out that the cause of pain in the rear was due to a few boils there....and took him to the vet again today morning. He's developed a bad rash (allergic reaction to his shampoo) in the area and hence the irritation/pain. He's on anti-allergens + antibiotics now and should be fine within a week. Phew. His fever isn't around anymore and his appetite is almost back. Which is all good news. Yay! Go Spike!