At 3 weeks old calf develpoed a cough and labored breathing. Had Vet out, we gave him Draxxin. Calf is now almost 6 weeks old cough and labored breathing have cleared up but it is still lethargic. He eats good but lays around a lot with his ears drooping and has a slight temp just on high side of normal. Talked to vet he suggested 5 days of penicillin for maybe a secondary infection. We did that no change. All his systems are functioning normal. This calf was very active and athletic. Any suggestions ?