I am sorry to hear you are worried about your Bulldog. My name is Rebecca. I am a veterinarian and will do my best to help.
Are his gums bright pink in color, or do they seem pale? Is he eating and drinking? Any coughing at all?
Panting can indicate pain, stress, fever, internal disesase, fluid in the lungs, high blood pressure. If his gums are pink, that is a sign he is getting enough air into his lungs.
Since there are so many things that can cause a dog to pant excessively, I start with a thorough physical exam: Check gum color, feel pulses, listen with a stethoscope, palpate internal organs and lymph nodes, take the temperature. If I hear fluid in the lungs, I take a chest Xray. Most of this you can't do at home, but can you check his gums and take his temperature and tell me what you find?