lower back cramps started eight days ago but now I also have some pressure in lower abdomin. feels like my uterus is heavy or a knot in it. Last LMP was 5-26-09 and started these menstral like cramps eight days ago...urine is clear...have had UTI's but it had never felt this. No burnig or pain when I pee. Also had lightheadedness two days ago and now very fatigued. Does anyone know what it might be?