Am I pregnant cause of my symptoms and negative test

Patient: Hope some one can answer this, My girlfriend had just finished her cycle on Nov 12, we were intimate on the 12th, 13th and 14th, but on the 14th she tool one plan b pill and then we were intimate later that evening and again throughout that weekend and parts of the next week. well a week after she took a pill for about three days she was having spotting and like blood when she peed but then it went away.and for the past 2 weeks she has been eating alot having headaches and urinating like crazy. Remember she only took the pill once and that was it. her period was supposed to start on the 7th of dec and nothing, she took a over the counter $7 pregnancy test and negative but still no period. SO is she pregnent or is it just a side effect of the one pill she took almost 4 weeks ago? Please help really want to know.

Symptoms: Hunger, headaches, urination