What Causes Missed Periods, White Discharge And Nausea?

i have not seen my period since April.My symptoms started in late may i had white Cheddar like discharge, lower abdominal pain that lasted for over a week. It's July and now its back but a little different i'm more tender down there and i had white Cheddar like discharge again it change an hour ago to clear and slimy with a hint of blood and I am also nauseous. I'm 21 and i never experienced this, I don't know what to do. Please help.