What Causes Lower Abdominal Pain, Headaches And Nausea After Periods?

Hi! My name is Jamie and my period was on dec 25, 2014. I started spotting on jan 11, 2015 at work. Then about 15-20 min later I bled through my work pants. It was a light pinkish color. After I bled through my work pants I was just spotting a brownish color.The spotting ended on jan 15, 2015. I have been getting really bad left lower abdominal pain, headaches, moody, breast tenderness, nauseous off and on, & sleepy. What could this be? I wasnt suppose to start my period until jan 22, 2015.