Start small and find a horse thag you trust. I used to be nervous at the canter, so I had to find a reliable horse that I knew wouldn't leave me dragging in the dust while I got my confidence. Sometimes you just gotta go for it.
Just take small steps and celebrate small victories. Don't push yourself and you'll find it works. I list confidence and I was pushed and I didn't get it back until like 6 months later. It helps to just go at your own pace.
Baby steps! Like Reagan said, start with a horse that will make you feel safe. Just keep practising and setting little goals, and don't rush it! Just take your time getting comfortable with something before moving onto the next thing! My confidence came back, so can yours!
I know exactly what you are going through. I was thrown off one pony over and over again and after that I was afraid. I only wanted to walk on some horses, walk and trot on others. Cantering scared me. One spook was all it took to make me get off. If the horse even thought about going faster I'd get off. I had to stop leasing one horse because she scared me. She was breath trained so when I tensed up she went faster. This went on for years. I lunged my 30+ year old horse before getting on. I developed many bad habits such as leaning forward out of fear. The key for *me* was finding the horse to help me. I started lessoning on a pony named Bob. He ran out of the arena with me a few times, he bulged, he put his head down and he spooked but I felt safe on him. He only gave me what I could handle and that helped me. It took years but i started noticing my confidence change. I cantered on Too Cute when I was too afraid to trot her. I jumped on Sonny tackless without lunging him. I started jumping Nina and I used to only want to trot her. It's been 7 years I would say and my confidence is greatly improved! I owe it all to my instructor Kim and the pony she put me on, Bob. It's different for everybody but here's what I would say to do. Find a horse that doesn't scare you, a horse you can trust 110%. He will help you with your confidence!
Hope this helped,