Anxiety disorder- please help me?

I just have to put a disclaimer before this- I would really like only mature people to respond to this, because I'm being completely serious, and being told "you're crazy" or "you just want attention" will probably make me start crying. :( I'm fifteen years old (I'll be sixteen in two weeks), and I'm female. I'm afraid that I have an anxiety disorder- I've been a worrier since I can remember, but my worries got really bad after I got my first period when I was thirteen. They subsided when I got into high school, but started up again badly six months ago. Ever since then, I haven't gotten any peace. Nothing reassures me, and even if I make myself not think of what's stressing me out (and it's usually something ridiculous and hypothetical, at that), a new worry pops up or the old one keeps nagging me. I used to be such a happy, optimistic person, but now I feel miserable and stressed. I feel even worse, because my mom sees just how stressed I am, and it worries her. I've tried everything I can do to stop- I thought I was smart deal with it myself. I'm constantly stressed out, or the thought is at least nagging at me, and it exhausts me beyond belief. Every day is a struggle. I'm Catholic and used to have a strong faith, but now even that is so doubtful, because I'm afraid that God isn't going to help me, or that this is His plan for me. I'm an A student and in all honors/ AP classes, as well as in choir, so I already have enough stress in my life without making more of it for myself. :( I'm going to start going to therapy over the summer, but I'm scared- will it ever get better? I don't like to think of myself as an anxiety-ridden person, and I know people usually associate mental disorders with self-centeredness, but I try so hard to keep strong for others and I'm afraid I'm just going to break. :( Thank you so much for reading this.