I'm sorry that you feel your academic performance this year has been below your expectations. However, I do ask that you spend some quality time with yourself, and really ask why it is that your marks fell below your medical school's threshold. Examine your social life, your personal life, and yourself, and be honest.
Clearly you are an intelligent individual, or else you would not have been accepted to medical school. However, intelligent people are first and foremost human beings, and the truth is that humans fail because of an innumerable variety of reasons. You really have to question yourself as to whether your motivation was high enough, whether your social situation is secure and conducive to studying, or whether you simply were sick and had a bad day during those exam blocks. I would also remind you, something I discover each and every day at medical school, is that academic marks have very little to do with clinical competancy. High marks do not imply clinical success.The people in the top 10% of your class might score more highly on their tests, but this doesn't guarantee that they will be great clinicians.
Finally, clinical confidence is often indicative of your overall confidence level. I don't think that most students ever get over the feeling of butterflies in the stomach. I know I don't. I think most people just conceal it, and move on. As to how you raise your confidence level, I can only suggest you examine your personal life to determine what went wrong on those examinations, and then smooth over your life before you get back to tackling medicine. You are a smart, and sensitive individual, and I know you can succeed.