If a green rider had brought this horse onto my yard as a boarder I'd be advising them to take it back ASAP.
You want to learn to be a good rider then initially you need a horse that's going to help you do that - not one that will challenge you every inch of the way and take advantage of your inexperience
If you're determined to stick it out then you must get a good trainer to work with that can watch and advise and tell you what you may be doing wrong so you know how to correct it and be sure you are actually asking the horse in the right way and not confusing it.
Clinton is full of good advice but PLEASE remember he is very experienced, very tough, very confident and strong and knows exactly where to place himself to stay out of trouble
Your horse was trained by bullying and aggression and horses like that soon figure out if a new owner isn't like that and they turn the tables and become the bullies themselves. They don't make the best 'first horses'
Hope you can work things out but don't forget riding is supposed to be fun