BB, when I left home, I remember shutting the lights the first few nights and feeling very alone. And my parens were only a half hour away by car. Still, when you're used to being with them, no matter how much you want to be "free", the child part of you may react with separation anxiety.
Expect that you might have these moments and don't let the anxiety scare you and escalate. It's kind of a primitive thing, and normal. You will adjust in time. If you have to call home a few times a day at first, then do it. I am way out of college and still yearn to hear my mom's voice for comfort especially when I am stressed.
As far as the bathroom thing, I agree with the other posters. Nothing wrong with going up to the teacher and asking what's the policy if you need the restroom, and then confiding in him/her that you have a bit of a nervous stomach, or IBS or however you want to phrase it..or just say "a condition that makes it necessary for me to go more often than others". I am SURE they would be nice about it. Lots of luck to you, this will be an exciting time for you, try to look at it in a real positive light and as you adjust, the IBS
may even improve.