What Causes Irregular Periods?

Hi, Since October I have having irregular periods, spotting and bleeding for only two days, unlike my usual 5-7 days. I have extrreme breast changes: tenderness, fullness, veins all over. I also just started having lower back pains along with lower abdominal aches. I have nause and light headedness with headaches. I have food aversions and sensitive to smell. I am also very tired lately. I have had two urine and 1 blood qualitative HCG tests and all three are negative. My NP thinks I am imagining things but I feel do bad. Please help!!!