How can you tell what is your period and what isn't? I took a plan b and one week later I got a withdrawal bleed one week later for about 8 days. I didn't feel any bloating, cranps or pain. Then a couple days after the withdrawal bleed I started bleeding again and it was a heavy flow with cramps and a backache that lasted 4 days that occurred feb 15th and I was supposed to get it on feb 17th. My thing is how do I know if it's my period?!