I was 11 when I first got my period, and I thought that I was well prepared for it. My mom is a nurse, and we'd talk before about what would happen and what I should expect, but when it actually came around, I had horrible menstrual cramps, migraines, and was so moody that I literally just laid in bed and cried for days. I was diagnosed with PMDD, a severe form of PMS, which is managed though anti-depressants and hormone therapy. Once I got on the right medications and learned more about my body, it got a lot easier.
I think a lot of girls get overwhelmed in the beginning. It's easy to feel unsure of what to do when you're dealing with all of these new concepts; tampons, pads, deodorant, acne, smells "down there", etc., but once you find a routine that works for you and learn more about your body and how your cycle works, you get more confident. You learn to deal with the cramps and the bloating over time, or you learn how to handle them with over the counter medicines like Midol or Tylenol, or you may even be like me and need something more than that, but you really do get used to it after a while.
It just takes time.