don't be afraid to adequately fuel yourself for you harder efforts.
other than that, in an otherwise healthy person, your lungs are doing the equivalent of what happens when you clean a fish tank. The water looks clear till you stir it up, and all the doo-doo gets stirred up and makes the water murky and cloudy. You'll clear out soon enough. up and out.
don't set 30lbs in 3 months.... just ride, be active and enjoy the result. if you get tons of miles in you, feel and look more physically fit and lose only 15 lbs, will you be disappointed? no.