Try reading some books on riding like Unrelenting by George Morris. Watching his clinics on youtube have also really helped me figure out what I need to fix in my fundamentals. You'll get there, good luck!
I would Lunge my horse over the poles a couple of times, then ride at a walk and then work you way up.
Yes! I agree with Jennifer, go back to the basics. Sometimes as riders we get so caught up in what we're doing that we forget our fundamentals. So take a deep breath, stay relaxed and confident (don't get frustrated!), and try something simple to freshen up on some old skills.
I would say not to give up and keep trying. Ride as often as possible and practice everything you know. I went through the same thing and learned that by asking my trainer for some extra help and dont be afraid to relearn basic things because it will only make you better in the end! Good Luck!