hi, Ive got a sharp knot in my lower abdomen which comes and goes for the last day or so, my last period was the 9-13 January. however have had 2 negative pregnancy tests , so doubt im pregnant, also back pain but this usually comes around the time of my period. also very tender nipples. anything to worry about? the woman at the sexual health clinic told me i probably didnt ovulate, but is that something to worry about? can this mean im infertile, im 19 and very worried.