I HAVE NOT HAD A MENSTRUAL IN TWO MONTHS BUT I AM NOT PREGNANT

I AM A 28 YEAR OLD MOTHER OF TWO CHILDREN, A BOY AND A GIRL, AGES 2 AND 1. I'M 5 FEET 6 INCHES TALL AND WEIGH 240 PONDS. I HAVE HIGH BLOOD PRESSURE IN WHICH I'M TAKING LISINOPRIL AND HYDROCHLOROTHIAZIDE 20MG/12.5 TABLETS TO CONTROL IT. I'M ALSO TAKING WELLBUTRIN XL 300MG. JUST ALL OF A SUDDEN I STOP HAVING A MENTRUAL. IT'S BEEN TWO MONTHS STRAIGHT NOW AND IM STARTING TO GET WORRIED. MY PREGNANCY TEST CAME OUT NEGATIVE AT THE DOCTERS OFFICE SO WHAT COULD IT BE. I JUST STARTED TAKING NECON 7/7/7 THIS FEBRUARY 2009. BEFORE THEN I WAS TAKING THE DEPO SHOT. WITH THE DEPO SHOT I UNDERSTOOD WHY I WASN'T HAVEN'T MENTRUALS BUT WHY NOT NOW. I HAVE LATELY BEEN FEELING PRESSURE IN MY CHEST RIGHT IN THE MIDDLE LIKE SOMETHING WAS SITTING THERE STUCK. I JUST THOUGHT IT WAS GAS SO EVERY NOW AND THEN I TAKE A ZANTAC. IF ANYONE HAS AN IDEAL OF WHATS GOING ON I WILL GREATLY APPRECIATE THE INFORMATION. THANK YOU