I am on birth control pills and have been for a few years. Recently, I started spotting a few days before period (4 or so) and off and on until my period. I got my normal period (5 days, heavy on the first few), but took a few hpts to ease my mind - all negative. About a week after my period, I am having lower back tightness when sitting around my tailbone (pretty sure I didn't hurt it). I took two more hpt two weeks after as I read this online - negative again. Could I be pregnant? Or what could cause the back pain?