Prolonged plan b effects?

I took plan b at the end of my cycle last month. My period came a week late which i know is normal. It was same length and heaviness. Anyways I am 2 weeks into my new cycle and my boobs are sore. And they have been sore since my last period ended. I took a pregnancy just to be sure even though I knew I was pregnant and it was negative. Is it possible to be side effects of the plan b hormones?