What Causes Delay In Periods?

I took the Plan B pill January 10. Got my regular period on January 21 for 5 days. Was suppose to get my period 3 days ago, but nothing. No cramps or anything. 2 pregnancy tests negative. 2 days ago I had a minute amount of blood like I was going to start. Nothing since except WATER! Literally clear fluid. Water like texture for 3 days now where my period should be. ??????