You have not mentioned your age, if pregnancy
is a possibility and if you are on any medication like hormones.
Presuming you are young, not likely to be pregnant and not on any medication, my feeling is that your hormones may be a bit unbalanced. It may be so because of some kind of pressure or stress
in your life at the moment-related to family, work or exams.
If all this settles down, do not worry as most women experience such upsets in their menstrual cycle sometimes. However, if it continues and the bleeding is heavy, make an appointment and see your gynaecologist for a check up.
I hope all goes well.