Could it be Anxiety, ADD, something else? Please Help :(?

Okay, so I am going to be Junior in college. My life is pretty good, I have an amazing boyfriend, my dog is the super cutest most adorable GSD ever. I am a mechanical engineering major with my summer internship for NASA studying Piezoelectric materials, great friends and family. I got a super financial aid package for next year. I have enough money to pay all my bills even though it gets a little tight every now and then, but overall I am proud of myself, I have a pretty good life, and I love it, which is all that matters right?
Recently I have been having a lot of trouble in school, the last few years I guess I should say. I love hiking, skiing, reading, swimming, tennis...okay so I have a lot of interests, I am not fat or anything, I weigh about 125 and am 5'6 so thats not too bad or anything, and most people would consider me kind of pretty. Not bragging, just back ground stuff.

I have problems concentrating, and I have major anxiety issues. I worry all the time, about everything.