Originally Posted by Bluemoonlvr
Thank you all. But the problem is that I do drop my stirrups and im perfect but when I put the stirrups back on I lose my seat
I've had the same problem where I can't sit the trot with my stirrups but I sit it perfectly without. What really helps me sit the trot (with and without stirrups) is to work from my core (your abs), to do this sit up tall, work on sinking deep into the saddle and absorb the movement with your core muscles. Most importantly don't tense up. Keep yourself relaxed and you will find it easier to sit the trot. The moment you become rigid and tense it will be harder to sit.
I'm a hunter/jumper but I learned this from taking two lessons from a dressage trainer. It actually helps a lot. I suggest finding a reputable dressage trainer, explaining you situation and they can help with your seat.
Hope that helps!