Unprotected sex 2/5, took plan b, then followed by sex with condom on 2/10. negative hpt this morning (first urine), 3/2. period 3-4 days late. could plan b be causing late period?

May be. It would be prudent to repeat the hpt in 4-5 days. You may get a blood test for HCG level that may settle the issue sooner. Pregnancy is unlikely in the scenario you described. Wish you good health!

"Plan B" will not cause a "late" period", and stress (emotional, job or school) can delay menses by delay of ovulation. At "50" , "pre-menopause" will cause significant delays in most women, secondary to the need for increased stimulation of ovaries before ovulation occurs, which adds time to the length of one's cycle....