I had my period, a week later bleed again 4 4 days i have had a constant lower back ache? stomach aches deep inside and headache, what could it be?

It appears you: Already have a diagnosis of endometriosis. It could be cramping made worse by endometriosis or even a bladder infection. First line treatment os a birth control pill to override your oen symptoms, this would help your chronic pain. Without a pill on board it becomes difficult to differentiate the source of your pain. Good luck.