Would you recommend an acting coach?

Okay, so I've always been told I'm a "great actress" from family and friends and teachers, but lately and a lot of times, I really don't feel like it. I have a low confidence level when I'm on stage and I become embarred when told I'm doing something completely wrong, and mad if I'm told it repeatedly. I love my drama teacher at my school, but I don't think she's helping me much. I have been thinking about having acting as a career as an adult, and hopefully going to Yale for that, but I know that I have to overcome my low self confidence on stage or when I do something wrong. But I need help with that, an dI don't know what or who else to turn to for that. And my grades are falling too, so that is making it even more once since I'm usually a strait A student. I don't know what to do. Robert Pattinson and Kristen Stewart are my idols at the moment because of how great of actors they are and how they got discovered (and because Twilight was THE BEST movie ever. I saw it tonight). And I was thinking maybe an acting coach would help me with that? What do they do? Could they help me with what I want? And also, I'm good at acting normal, like people do in movies and stuff, or romance stuff, but the totally dramatic "NOOO!" moment when someone dies or something, I can't do. It's just awkward. I can't do the sobbing "boo hoo" totally over the top dramatic stuff. Just like the movie stuff I've noticed. And we are doing Our Town s our school play and I got the lead Emily and the end she's all "goodbye world!" and stuff, and it's weird. Could an acting coach help me with all of this? I would really like to pursue my dreams.