hi there.
whats happening is normal,... periods can be irregular for years before they regulate, most women have a period every 28 days, but this varies some can be unlucky and have a period every 21 days.. others like me have a period every 35 days so we are all different, the amount of blood you lose also changes from light medium to heavy flow.
you will get use to what your periods are like, if your worried about bleeding onto bedding you can buypads especially for night time, and you could put an old towel or sheet on your bed to protect it.
im afraid most women will have the odd accident, but as i say you are going through a normal process of your periods and you will soon learn when you are due on. write down the date of your next period from the first day of bleeding the when its finished write down your next one you will soon be able to count how many days you go between periods.
hope this helps
deb