I'm 18 years old, had a daughter in Dec of 2010. After my cycle in July I didn't have a period for a little over 2 months, took multiple pregnancy tests and they were always negative. Then come late sept I had my period, lasted 3 -4 days. Then my period a week and a half early in oct, which my period is always a few days or a week late, and I've been bleeding lightly ever since and today is day 16. I just have lower back pain and very exhausted and it's starting to scare me.

Best to see your doctor for an exam. They will do another pregnancy test in the office, and possibly have a blood test done for pregnancy as well. They may also decide to do an ultrasound to determine a possible cause.