Intermittent Shortness of breath.

Hi Doctors, I am 25 years old and i am highly active in terms of exercise. I go to the gym 5-6 days a week and have never faced breathing issues. I could easily run 3 km without taking a break, but all of a sudden, for a week, i have been having breathing problems. This is what happens- I breathe normally for a 5-10 min, but suddenly i feel like i am out of breath and feel like breathing really heavily. I breathe heavily and sometimes i have to breathe twice or thrice heavily to feel better. Please also note that i am a light smoker - i smoke from 1-3 cigarettes a day. On weekends its only 1 cig a day. The smoking has been ongoing for about 6-7 months. I've never faced such an issue before, and this is happening all of a sudden. Also, i eat around 5 eggs a day and have chicken during lunch. I had gotten a test done for cholestrol and it was pretty high. Could that be an issue? Heart problem? Please help me understand what could be causing this.