Period Started One Week Late With Severe Cramping Lasting Three Days

Just wondering if anyone had, is or can explain these crazy symptoms I am experiencing.  I have just gave birth about 5 months ago now. My period started about three months ago. All on time and normal.  I noticed after the fact that I had sex on my most fertile day on the 1st of Nov.  This month I notice my period was almost a week late so I took two pregnancy tests a few days apart both coming out at negative. I finally start my period which started off as light an pink at 3am that morning. Later on into the day I noticed severe headache and cramping so bad I started taking ibuprofen 800 mg every 6 hours which did nothing for any of my headache or cramping. I was hurting so bad I felt like going to the emergency room last night. I had a really heavy flow for a day. The next day I noticed it getting lighter but was still having severe symptoms. Today the pain is more bearable and my bleeding is very minimal spots and brown.  I have an appointment tomorrow with my doctor but was wondering in the meantime if anyone has experienced these problems and your input on it.