Reading the first post, I understand that there is more than one problem. Shaytan is attacking you in many ways. Every thing, every thought, doubt, image, or inspiration that comes from him is recycled, you are not alone is what you are experiencing, but you are quite strong in asking for assistance. May Allah (SWT) assist you to near him. In my experience, the following will help relieve your condition.
He attacks you because of lack of knowledge of Allah - The best cure is the opposite, which is knowledge of Allah, his attributes, and his perfection. You must know all of the ninety-nine names in this book: ghazali.org/books/Ghazali-99-Name-of-God.pdf. Read them every morning after Fajr with the correct understanding. It will bring a light into your heart that will repel Shaytan's darkness and weaken the strength of his words. Reciting Surah Yasin every day after Fajr is a source of light and protection from Shaytan.
Why his whispers are especially potent - They are strong or weak in relation to the following: your sins; what things are dear to your heart that are his property such as music, blameworthy traits such as malice, greed, envy; your level of physcial cleanliness; how much and what kind of food you eat; what your goals in life are. All of these indicate something more important.
At the core of the issue is how much light you have from Allah. This light is in your heart. Without it, your dhikr and arguing with Shaytan won't repel him. Ghazali wrote in this book: ghazali.org/books/skillie.pdf that a man once saw himself in a dream. Shaytan was leaping at him. The man picked up a stick to ward him off, but he heard a voice tell him that Shaytan is not afraid of that, he is only afraid of the light that is in the heart. It's enough right now for you to know that light comes from Allah, and it grows when we are sincere in prayer, exercise patience in adversity, recite the Qur'an properly,and other acts. It reduceswhen we sin.It guides our actions and thoughts. It also fuels the words that we recite. Asdescribed by Ghazali, peoplemust understand that Shaytan is only afraid of the light that is inthe heart of every believer that fuels our speech and repels him, notjust the sounds by themselves.
The things mentioned earlier reduce your light and strengthen Shaytan's voice and ability. The solution is to cultivate your light. I can tell you with certainty that it will wear Shaytan away because his corrupt words, suggestions, darkness, and other tools cannot remain where there is light from Allah. Along with understanding the ninety-nine names and Surah Yasin, I recommend the following:
Clean your heart - Think of all of the wrong you have ever done. Do istigfar as your recall the sin. Think of all the people you may have hurt and who may have hurt you, and ask Allah that anyone you may have wronged forgive you, and that you forgive every one that has every wronged you. If you've never made this prayer, you will know it's correctness when you make it. Gradually implement the sunnah in the other areas, such as giving up things which are not your concern, avoiding the gray areas, opposing bad character traits, and others mentioned by Ghazali. Without cleaning it, he roams freely in your heart, saying whatever he pleases, and your words are ineffective.
Be physically clean - apart from showering, remember to cut your nails, removing pubic and underarm hair. I must tell you that brushing your teeth, with just a tiny amount of toothpaste is fine, right before prayer or after eating anything will weaken Shaytan's ability.
Don't eat junk food - Eating what a Muslim has made is always preferable because it has more blessings and less of Shaytan's influence. Eating too much will strengthen his ability and suggestions. Remember to say the du'a before eating.
Set good intentions in life and in fact before every action - If you're going to school, do it to please Allah. Constantly being in a state of remembering Allah will make your heart an unappealing place for Shaytan which will weaken his suggestions and his influence over your heart. Intentions not only make you feel good inside, they have consequences. Allah assist and rewards people based on their intentions. You may have angels that assist you on your way to school and ward of Shaytan simply because you made a good intention.
At its core, you must build your light from Allah. The suggestions above will help. Please consider these things and update us on how you are doing.
Wa Assalamu Alaikum Wa Rahmatullahi Wa Barakatuhu