help please...

Kayla

So I'm 21 days late... I took a test a week and a half after my period was due and got not pregnant! A week after that I took one again and got the same thing... i did takw plan b one srep early in my cycle! but I ran 1.5 miles today at school and on my 4/5 lap i started getting cramps... they lasted for about 3 hours now there gone! how long do you think it'll take for my period to come?...