Echo shows Calcification of aortic valve & thickened mitral valve, BP stays 140/100 or higher. Short of breath and fatigue. What could be the cause?

Work up. smoker? Pulmonary function? Weight? Anemia? Exercise tolerance? May need cardiac cath as well to determine any associated coronary disease.
Atherosclerosis. What you described, high blood pressure and calcification of valves is suggestive of atherosclerosis that is likely affecting the coronary arteries and you may be in heart failure. Please consult your doctor at the earliest.