Is it normal for anxiety to make physical exercise harder (and to easily make you out of breath)?

Hey everyone. I'm 16, and panic disorder (which runs in my family) has really been taking control of me for the past 3 weeks. At least, that's what my family is positive it is. I feel like my life has been taken away from me :-(. I went to the doctor to get an EKG, blood test, and chest x-ray to rule out anything else and was told that I'm as healthy as a horse. I've been on Lexapro and Ativan for 2.5 weeks which have helped me a bit but I'm still waiting for a full effect, as I'm not getting full-blown panic attacks as much but am still experiencing a lot of breathing troubles, which are extremely uncomfortable. I also noticed that I easily get out of breath when just doing small physical exercise. I just wanted to make sure this is normal since I'm extremely paranoid about my health, despite the fact that I was told I'm healthy. I'm so afraid. Thanks to anyone who can help.