Severe Pain After Physical Exertion, Popping Sound, Discomfort, Hamstring Pain. Is This Serious?

Hi Doc

I was doing my routine split stretches and when i went down into my split i pushed further down to the floor. As i went down i heard a popping sound, like bubbles popping in a line. i had no severe pain after that, but an uncomfortable sensation in my upper leg. It was not my knee, hip or groin. My hamstring does not hurt. The pain feels more upward toward my buttocks, just under the buttocks. More to the side as well. it is uncomfortable to walk and it hurts to make my leg straight and point my toes. Usually when i put my feet next to one another. keeping my legs straight and i stretch down i can easily touch the floor, now it is difficult. What muscle could i probably have torn or hurt and is it serious?

thanks Melissa