You are not alone. The Bible verse quoted with Paul's words show that even the most faithful still have such moments of struggle. Isn't it helpful to know that we never struggle alone. All of us are born with a sinful nature, we've all been poisoned by sin and are incapable of overcoming this poison on our own strength. The fact is we need a cure, an anti-venom, a doctor.
The good news is we can be. That's why God became a man in the person of Jesus. He is the Great Physician and came to save us from this deadly poison of sin. He forgives us and gives us the power to overcome what we can't defeat with our own strength.
He provides the Holy Spirit to do what we ought to do by giving us the inner desire and discipline to want to. It's found through faith--faith in Jesus Christ. He gives us the victory that we can never give ourselves.
Allow God to be your Cure!