My sister had heart palps and shortness of breath pretty badly when she was pg with her 2nd child and was in and out of doctors and hospital until they worked out what it was.She was very anaemic and lacking iron and had to have iron injections.
My sister was a vegetarian but she had to start eating red meat,took iron tablets and she was fine,baby was beautiful and healthy.
You should go see your gp.
All the best
Michelle