I am another person who has this same trouble ~ I always have.
15 years after kicking my panic disorder, and I still cannot focus on my breathing. Doing so makes my breath all mixed up & then I start hyperventilating!
What does work for me in relaxation exercises is visualization. I fully involve myself in the exercise (with as many senses as possible being stimulated). A favorite: Imagine a forest, with big tall pine trees. They're close together, but you can see spots of blue sky and sunshine rays coming through the spots without trees. Take a deep breath and you can smell the pine in the air. It smells so good and refreshing! There is a small walking path through the mountain area. You walk along the path, hearing pine needles break & pine cones fall from the trees as you walk along. The air feels comfortably cool. As you continue your walk through the mountain, you can also hear the sound of flowing water. The sound is becoming louder and louder, the trees grouping is also becoming more sporadic. The sunlight area is therefore larger. It feels good to have the sunshine kissing your body. Warming your scalp, arms, and face. A-ha! You see a small stream on your walk, and decide to follow it for a little while. After walking for another mile or so, the stream widens and slows down. You decide to stop and watch the stream for a little while, sitting alongside the water. The stream is crystal clear. You can see big and small rocks in the water. Little pebbles, covered in a bit of algae, rocking back and forth. Bits of tree bark and sticks occasionally flow along the stream. Squirrels run around and pine cones continue to fall from the trees. Very peaceful. You enjoy this mountainside.
Whenever you're ready, you can walk back to your car. Slowly smiling, completely enjoying being in that moment. You can come back any time. It's always there for you.
That is a personal favorite of mine. It does help put me into a much calmer state of mind, when I need that. Just think of all of the fun and calm things that you can do out on the mountain! You can skip stones; go for a hike and get lots of pictures taken of the beauty for you to look back upon; camp out & imagine relaxing beside the fire; the list goes on!
I hope that I haven't triggered anyone in my description..and I REALLY hope that I have given you some ideas that do help relax you. Very gentle hugs & best wishes to you!