I am sorry to hear you are worried about Buddy. My name is Rebecca. I am a veterinarian and will do my best to help.
It is a good sign that his nose is moist and he has a good appetite. Still, can you take his temperature with a thermometer? That is the only way to be sure he does not have a fever.
Is the limp worse or better today? If you check his gums, are they bright pink in color or do they seem pale?
Listlessness and limping can be signs of tick disease such as Lyme disease or Ehrlichiosis. It can also be an infection in the leg, or pain. If I could, I would start with a thorough physical exam: feel his pulses, check his gums, take his temp, palpate lymph nodes and internal organs, feel every joint and muscle and bone in the lame leg, listen to him with a stethoscope.
If he is eating, and his limp gets worse, you could try aspirin. I need to know his weight to give you a safe dose.
Let me know what other questions I can answer.