In this month i have 2 periods in 8days gap What is the reason behind it? why this is happend?

In this month my periods comes on 13th may 2011 & finished on 16 th may 2011 after that on 22nd may i went to Bombay for my official meeting. When i return back on 24th of may again start the periods with better flow. Why this is happens? Why the period comes again with very short interval