Anyone having a hard time breathing?

My chest has grown quite large already, but for some reason I feel like I just can't catch my breath. I have been walking and excercising and was doing that before we got pregnant. But this is completely different than my other two pregnancies. I haven't technically put on any weight but you can definitely tell if I wear a tight shirt. I feel like a balloon ? no other real symptoms just wondering why this is causing me so much trouble.