Lungs feel heavy, hard to breathe, but no coughs?

My lungs feel heavy and I now have a sore throat. However, I have no coughs so that rules out bronchitis. I have a history of asthma and yesterday, I did physical activity which I haven't done in about 2 years. Could that be the reason why my lungs feel so heavy and weak, because I am out of shape? The only other possibility was that during mountain biking, I inhaled alot of irritants in the air. I went through alot of brush, flowers, thorns, trees, tons of dirt you name it. The weather was particularly hot in San Dimas, CA.