Shortness of breath?

I'm fairly active. I run almost everyday ... around 3 miles or so and train on the weekends for a half marathon. 5 - 8 miles usually. I am obese but I feel fairly healthy (I have my share of slips with food). Over Thanksgiving week  (plus a few days) I gained 10 lbs, which isn't rare at all. I gain and lose 10/12 lbs at the drop of a hat. But lately, I'd say for the past 4 days, I've been extrodinarily out of breath! The stairs today almost killed me! I huffing as I sit here and type this. I'm 9 dpo and have been TTC for #2 for 3 months now. Could this possibly be an early pregnancy sign? Or just a direct impact of the extra weight? Any advice out there?