03 CAVALIER LS Problems with starting

My Cavalier will not turn on. Before, it would take it a while to ignite and if it did it felt like it was about to turn off. It would only stay on if I added alot of gas. Now it won't start at all. It seems like it has something to do with the fuel line or pump. I put some of that octane booster in it but it didn't work. Any suggestions before I have it towed to a mechanic? I would like to have an idea before they try to rip me off. Thank you.