Mitral valve regurgitation is usually mild and progresses slowly. You may have no symptoms for decades and be unaware that you have this condition. Lightheadedness can be a symptom of MVR. I have moderate to severe MVR and no symptoms, but your symptom is listed as a possible effect.
You should have your doctor rule out any problem because sometimes, the problem develops quickly, and you may experience a sudden onset of more-severe signs and symptoms. Your pregnancy may be involved so I have provided a link that discusses that aspect. Hope this helps, and thanks for sharing.
http://www.medhelp.org/posts/Heart-Disease/mitral-valve-and-pregnancy/show/254107