You say you've had irregular periods for a long time, but also say they came every month at the end of the month - so that sounds very regular! They are extremely short, which is something you should have discussed with your doctor. There are all kinds of things that happen with hormones that affect both the timing of your periods, their duration and the amount of menstrual flow (which is a result of how much endometrial lining builds up during the month).
You don't say if you are using any type of contraception now. Hormonal forms of birth control can affect your body, but not using a reliable form can also obviously result in pregnancy at higher rates. Is there any possibility that you are pregnant again?
Can you tell us what you have discussed with your doctor? I'm not sure how you expect moms on the internet to tell you when you will get another period when we don't know anything about your medical history, your birth control methods, or what has already been done/discussed/ruled out with your doctor.
If you are not absolutely positive that you aren't pregnant, then use a non-hormonal form of birth control now. And give your OB/GYN a call on Monday morning. You can make free calls to that office anytime, and they will help you decide if you need to be seen.