I have constant feelings of doubt in magic. I constantly tell myself that I do believe in it, however I feel that I don't and only think that I do due to fear of Allah. A few days ago I had this thought "If I really do believe can I swear by Allah that it is true?" And I couldn't bring myself to do so. Am I a disbeliever and if I am, how do I start believing?
There should be no doubt or hesitance in affirming the teachings of Islam. This is definitely an issue which you urgently need to overcome, as true doubt is Kufr. -- But maybe you are ignorant on this topic and knowledge will quell these evil thoughts?
Strengthening your Islamic knowledge and logic/reason is the way to overcome this issue. -- Magic is real. It can affect people physically. Some of the most truthful people (including the Prophet (ﷺ) himself) were afflicted by magic.. experiencing what they were not going through, among other things; they didn't just make these things up. And Ruqyah helped counter symptoms of magic.
Moreover, the Creator who made everything would know what is real or not. Magic is subject to His Will too. He said it is real and that those who engage in it (to hurt others, etc) are disbelievers. Magicians often utilize Jinn, whom we are forbidden to turn to.
Refer to people of knowledge/scholars to help you further. Or feel free to ask more questions here if you have them. May Allah (ﷻ) guide us all and keep us firm on Islam.