Something is wrong with my dog?

Something is wrong with my dog and I wanted to know if this is normal or not. She's about two and half years old and she ate like half of one pound piece of chocolate and er and ate a burger. Well she has been losing alot of weight and she looks boning, looks like she lose her muscle or something you can feel her ribcage and her spine and there's like very little muscle around it. She also hasnt been eating much barely anything for about close to two months, but now since about two to three weeks ago she has finally started to eat. But anyways does anyone know what could be wrong? Is she dying slowly? Or should I just try to help her gain her muscle back, by taking for walks and runs? Need help! What should I do?