Other reasons for a late period?

I have always had a pretty regular period, this month it's 6 days late as of now. The first day of my last period was Jan. 28, it lasted 5 days like always. My cycles are about 22-25 days long. I'm afraid I may be pregnant & am hoping it's just severe stress (although I've never had this problem).. Also* I'm 21 & do have one child. Could it be stress, or something else...?