What Causes Painful Period With Nausea And Stomach Flu?

Hi, I am a woman. I am 37, have been feeling weak and very weary recently. Sleep a lot but always feel as not enough, wake up tired. Force myself to do things. Also mood change, turn into a beast closer to my period days, sex is painful in some positions, often pain in lower stomach and back. Last menstruations were painful, more abundant and with big clots. A month ago had probably a stomach flu, still have nausea, feeling of full stomach after a small meal, throwing up. Blood test revealed all normal and a little low WBC. Could you advice what kind of tests will clarify what s up with me.