At this point, I cannot offer you a 100% definitive answer, but I will do my best to tell you what Scripture says to this effect, and offer my best shot at an opinion. I do know that God has begun a good work in me, and will perfect it (Philippians 1:6). Our sanctification began by the regenerating work of the spirit, and cannot be perfected by our own efforts in the flesh (Galatians 3:3). So for sure, God is the one who drives our sanctification. However, we are still responsible for our actions, otherwise there would be no commands to obey God’s commands, consider ourselves dead to sin, and to stop sinning (Romans 6; 1 Corinthians 2, 10; Galatians 5; Ephesians 4, etc.).
See, there is this tension in Scripture that we find throughout Paul’s letters… there’s a sense of Christians already having the perfecting power of the Holy Spirit inside of us, but we are not yet perfected – that will only be when we are in heaven for eternity. It’s called the ‘already/not-yet’ paradox, and there have been many books written about it as well as the interaction between God’s sovereignty and human responsibility.
The best thing that I can tell you from this point on is to fall on your face before the sovereignty of God and pour your heart into your relationship with him. Pray constantly that he will continue to drive your sanctification and trust that the Holy Spirit (God himself) is enough to help you as you live your life.
As far as knowing when you’re walking by the Spirit as opposed to gratifying your flesh, read the Scriptures and figure out what God’s heart is and where your convictions lie. Also, find a solid church that can teach you and sharpen your walk with the Lord, and get plugged in with a group of people who love you and who you will let speak into your life with authority, and hold each other accountable. Trust that God will convict you of sin, pray that he would open your eyes to it, and lean on the grace of Christ when (not if) you find it in your life. That, as far as I can tell, is how we can humbly work out our salvation with fear and trembling (Philippians 2:12).
As a final reference, I would encourage you to read Romans 6-8 (especially 8:1-17).