I only have menses for 4 days and on fifth day i have little bit of brown spotting. is this normal?

Probably: Pcos is a condition where there is a tendency to have changes in the menses. Lower estrogen levels can lead to a lower amount of thickening of the lining of the uterus or shorter and lighter menses. Pcos can also results in cycles where you do not ovulate and then only small areas of the lining lift off at intervals leading to spotting or periods like you describe.