It could also be purely coincidental (though I hope for your sake that it was just the B.C.) You are approaching the age where most adults develop their anxiety, and you have some big life-events ahead of you. Yes you are excited about your wedding, but it is still a big change and can help to tip you in the direction of anxiety disorder.
Although you have come to the right forum for your anxiety, I'm not wondering if you should make a stop over on the Birth Control Forum and see if there are other women going through what you are. I don't really know anything about birth control, being an old croan long past menopause, the advice of other younger women may be more beneficial to you. I really don't have a clue if your bc could be causing your anxiety. My guess is that it's very possible, but I would strongly urge you to see your ob/gyn and discuss these feelings with him/her.
Anxiety is a terrible disorder and when you say you are now having doubts about your marriage, I would tend to put those down to the anxiety and perhaps a little bit of the "cold feet" syndrome. But, you need to take this to your doc, the only one qualifed to ascertain what is going on with you physically. While you're there, make sure you have a good long talk about your recent advent of anxiety.
So, make a dr appt. and check out the bc forum. If you are still feeling anxiety, please don't hesitate to come back to us! There are many young women on this forum and they may have just the answer you need! I wish you luck as this should be one of the most wonderful and exciting times of your life..........hectic, crazy, chaotic.......yes, but not filled with anxiety.
Keep us posted, OK?
Peace
Greenlydia