I have! I'm not really showing at all, so my doctor ran some tests and since my lungs were clear and my blood pressure was fine, he thinks it's just the way the baby is pushing my organs up is putting pressure on my diaphragm so my normal breaths aren't as deep as they should be. It results in every once in a while I have to gasp a little because I feel like I've been holding my breath. He said that if I were carrying more outward it might not be a problem, and when I "pop" and start growing out it might alleviate it but for now he believes it's just one of those discomforts of pregnancy.
Depending on what your tests show, your doctor might find the results different, though. Sorry you're having trouble with it!