What Causes Bloating, Cramps And Nausea With HPT Negative?

I have been to the hospital they did an ultrasound, blood and urine test that said neg. for pregnancy, cancer and cysts, but I am bloated my back hurts when standing for a long period of time I am nauseated, I have sometimes cramping I need help. I am 26 I have had 4 kids already but never had negative tests