Missed Periods, Stomach Cramps, Lower Back, Pelvic Pain, Clear Vaginal Discharge. Causes For Symptoms?

I have not had a period in almost three months. I have been having cramps in the lower stomach and lower back pains. I have also been having aching in my pelvic area and tingling in my nipples. I have a discharge that has no smell or color. I am 31 years old 5 4 and weigh about 122 pounds. I have five boys the youngest is six years old and my husband had a vasectomy in Dec of 2007. Can you tell me what could possibly be wrong with me?