I have had irregular periods most of my menstrual years. I am 23 yrs old. I have however had normal periods this past year. NO period in August and on Monday had what I thought was a period. It started pink then red with clots and then brown. Gone in 24 hours. Now I have lower left side pain near ovary and lower back hurts. Had negative hpt, quantative blood test, and no signs on sonogram. What can this be? Has anyone had this and be pregnant?