If Tested Negative For Pregnancy What Causes Delayed Menstruation And Vaginal Discharge?

I havent had my period since March and for two months now I have experienced vaginal discharge clear and around the time of my period. slight cramping, lower back pain, breast swollen, nausea almost everday, and fatigue. I took two home pregnancy tests and both say negative. I am 26 years old so im sure im not going through menopause and I get a STD and STI check up regularly... what else could it be?