Constricted thoat, shortness of breath when doing anything physical

I am a 30 year old female who's been fairly active all my life, i've been a social smoker who recently quit smoking. I am somewhat out of shape, approximately 15 - 20 lbs over weight...I've been about 10 -15 lbs over weight thru my 20's and it never effected my breathing. But recently if I do any type of jogging or running at all I suddenly experience major shortness of breath and it feels like my throat is closing up and like I am almost gasping for air. I havent ever had any chest problems or lung problems before accept for some irregular heartbeats occassionally over the past couple of years, which were random and may have been stress related. This is worrying me...any idea of what it may be?