Speculation: Suck it up! You're probably out of shape.
My thought too.
Stick with it for a few weeks, if it gets worse, see a doctor.
But IMO, people in todays modern world are looking too quick for a quick fix via medications.
They think they got asthma or something, when they may just be out of shape.
Hang in there, if it's not getting better, see a doctor.
-Hedge