Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today.
Any gagging, retching, lip licking, drooling or vomiting?
What does the diarrhea look like? Any blood or black material?
Are his gums pink or pale/white? Moist or sticky?
If you press on his belly, does he have any discomfort, tenderness, or tensing?
Could he have eaten something he should not have (ie bones, toys, rocks, plants, chemicals, etc)?
Since you noted that he is breathing heavy, can you take a breathing rate for me (just count his breaths for 10 seconds + multiply that by 6)?