I had covid 3 weeks ago felt fine now i have shortness of breathe my oxygen is fine lungs clear chest x-ray clear and ekg clear could it just be a cold or lingering covid symptoms or my anxiety its like i have to yawn to breathe?

If your shortness of breath is at rest and not during exertion, anxiety is the usual cause. However if you're short of breath with activities that shouldn't make you dyspneic & there's no cardiac cause or anemia,, I recommend consulting a pulmonologist for evaluation. Appropriate testing will most likely include a chest CT scan and pulmonary function testing.