Is it normal to have periods twice in single menstrual cycle?
The menstrual cycle is the full reproductive cycle from one period to the next. You can't have two periods in one cycle, either you have a shorter than normal cycle or you're bleeding for a reason other than menstruation. If your cycles are shorter than they should be or you're bleeding mid cycle then talk to your doctor to determine what is happening to cause this irregular bleeding.
If you are on the pill, you should call your doctor about it. You may need to get on a different kind. If you missed or were late taking the pill, that could be why also. If it just happened this month and you aren't on the pill it's probably just a weird thing. If it happens a lot, you should talk to your doctor. You should only be having one period a month.