I hope you will continue to talk to your therapist about this. I suspect the frequent moves have had more impact than you think. Yes. Other people have moved more, but you are only 13 and have already moved 3 times. I have heard the same reaction from military kids and from kids whose parents have made frequent moves due to jobs. It’s as if a part of you is already getting ready for the next move.
The first thing to do is to talk to your parents about whether this move is the last one for a while. If so, you can relax into this place. If not, then talk to your therapist about how to embrace the new experiences and new people you meet at each place. Frequent moves do often cause feelings of loss. But they can also be seen as opportunities.
I wish you well.