Had 2 viral infections back to back still have second. lungs sound clear but short of breath worse when laying down.scared it's myocarditis?

Get it checked out: If short of breath, then best to get it checked out by a primary care physician or cardiologist. Still far and away the greater likelihood is that the infection has given you temporary respiratory impairment. But a health care professional can assist you in determining whether or not you have developed a bacterial superinfection worthy of antibiotics, or if you need an echocardiogram.