Oil loss

I have a 2001 chevy silverado 1500, it has 104352 miles. And its a v-8 automatic. My questions is about oil and antifreeze. The past couple weeks I have bought about 9 quarts of oil. One day the light came on so I put some more in but the lgiht has satyed on, I will put 1/2 a quart in, in the morning and in the afternoon it will be really low, and I dont drive it for lunch. It has been to the shop about 3 or 4 times but they give it back and say there is nothing wrong with it. I dont know what to do anymore, I am a student, and dont ahve that much money and have to stop buying oil, what do you think is wrong