Go to Confession as soon as possible. Having fallen so close to Confirmation must surely add to your sense of shame, but it does not objectively change the nature of the sin.
Porn should be treated like heroin or opioid drugs: it has an effect on the brain that can change it, especially during development as in your teen years, and can harm you for the rest of your life. I am not exaggerating, this is based on research. You should find a good Christian friend and form an accountability partner, someone you can trust and confide in when you are feeling tempted, and help you through the tough times. Don't take it lightly; porn is a plague that is destroying relationships and enslaving people.
Get out of the vicious cycle that leads to addiction and get help. Pray for strength and wisdom and God will be there for you; he is not an angry Father waiting to shame you, but a loving savior that wants to free you from slavery and pain.
This is not something to take lightly, but don't worry you are not alone, this porn madness is capturing millions, both and women, and our culture is creating the problem, saying it's okay and then abandoning people to the vice. Don't believe the lie; there is hope in Christ and you can be free.
Confession is the first step.