What Causes Spotting And Lower Back Pain?

i am a 35yrs old female im 5'9 160lbs have noticed blood on the paper when i wipe its light pink and i have been getting this lower back pain as well what could it be its been happening for 5 days now? i was diagnosed in 2000 with edometriosis and concieved a child in 04 i havent had no symptoms in regards to that . Till now that im experiencing this and i already had my cycle on the 7th of this month. What can be wrong?