Hello
You've seen a physician, and she's pronounced you fine, which I assume means "not pregnant." If you want to set your mind at ease, I suggest you purchase a home pregnancy kit to alleviate your worries. Dr. J
I would not be worried. You still seem pretty on cycle. Plan B may have altered your normal cycle a lil', too. It's normal to be worried but I would TRY not to stress out about it. I know it sounds like an old wive's tale, but stressing can make you later than normal.