Why My Menstrual Periods Are Missing?

Back in march i thought i was pregnant, but i started my period and didn't think anything of it. Since then i have not had a period its been about 3 months. I have taken two hpt and both have came back negative. i read online about how low horomones can cause hpt to come back neg. i have also read about symptoms all of mine have been weight loss, then here recently i have gained weight only in my waist line, constipation, color change around my nipples, frequent urination, my back has been hurting, and discharge.. what should i do??