What is your opinion?

My last period was may 19. For about a month now I have had fatigue, nausea, vomiting,headaches, stomach pains sometimes a cramping feeling sometimes it is a sharp stabbing pain above my belly button. I have been constipated for about a week now and have been peeing a lot more than usual and I have been more moody I cry a lot more than usual and at the littlest things.my next period was due june 16 but it never came. I took 2 tests a week after my missed period and both came up negative. Could this be pregnancy or something more serious?