What Causes Reddish Marks Under Stomach With Discomfort In Stomach?

Hi. I took plan b this last monday and I am freaking out. ive never been so scared in my life before. i took a pregnancy test the day i took the pill and it said negative. by the way i took plan b pill less then 24 hours. today is my third offical day on it and my stomach feels a little weird inside. Its been feeling like that all day yesterday and today. but the same day i took plan b i felt very extremely bloaded. Im so worried i want to have my next period already. By the way I just got off my period last sunday the day it all happend. Why does my stomach feel weird and im starting to notice reddish/dark/purpleish strech marks underneeth it.