I have a feeling she just can't get over the fact that I am not a little kid anymore. (14, by the way)
No offense, but you are in the age group that is in the most need of parental supervision. You haven't quite reached a mature age yet, even if you are more mature than other 14 year olds, you still have a lot of growing up to do. Give your mom some time, and show her that you are responsible and she'll come around.
As for the sleeping arrangements, you should really have some privacy. I know your mom probably is trying to be protective, but in this case, she's really harming your sense of privacy, which is needed.