What Causes Vaginal Spotting, Cramps And Frequent Urination?

Hello,I have been spotting between periods and having excruciating cramps since December and my period comes between the 3rd and 4th of each month. This month I have not yet started my period nor had any of the symptoms I usually have when my period is due.I am getting symptoms such as bloating, even thought I have lost 8lbs my trousers are tight around my stomach, I am urinating a lot often, my breasts are tender and I have lower back ache. I also feel different in myself as well as craving foods and disliking foods I usually always eat.My blood tests show nothing and pregnancy tests are negative and I had both of these last month. Please help! I know a lot of people who have had pregnancies without positive tests or the HCg showing up in a blood test.