Ceasar certainly sounds like he is in trouble and needs intervention, quickly. Without more background information, and photos, it is impossible to give more advice. However, with any sick animal, heat and
hydration are of primary concern during a health crisis. When The immediate crisis is over, and he is warm and
hydrated, it will be time to address his overall care, like heating, lighting, UVB, and nutrition. What tests did the vet give? What were the test results? What shots did Ceasar get? Was it a vet that specialises in reptile care? There are many possible causes of weakness, lack of appetite, and sluggishnes, including brumation (which is natural and not usually a health crisis) disease, injury,, metabolic issues, UVB deficiency...the list goes on. More info is needed, to make any guess about cause, or any specific recommendations.I woild not hesitate to return him to a good reptile vet asap.