i am 17 years old, 5"3, i weigh 102 llbs now, i used to weigh around 110 llbs, but for the past 2-3 weeks i have been feeling very nauseous, sometimes vomiting, cant eat that much, sometimes its really hard to go to the bathroom, and sometimes i have black stool, (its kind of scaring me, ive never had that before) i've recently went for blood tests , and a urination test thing, but i've gotten no calls back from it. i have also recently changed my birth control two months ago, from yazmin to ortho tri-cyclen could it be that or something more serious?