Hi
I have problems with my period too sometimes i would get it twice a month. In the past 2 yrs 3 times a yr i would get it twice a month i went to see my doctor and everything was normal had a pap smear test and everything was fine it's just that everyone is different. Sometimes i would be a week early than last month sometimes 10 days later so it's nothing bad. ur doctor might put u on birth control pills if you want to regulate ur period. I was on birth control and when im suppose to be on my period pill im always behind so ......
typically when a period becomes earlier and earlier, the follicular phase of the cycle is shortening. it is impossible to tell it that's happening with you over a forum, and your doctor will likely suggest testing.
I'm not sure if this is much help, but if you are still worried i would try finding another doctor who can see you sooner. Good luck.