Hey Bahy, it can be frustrating when you don’t feel you are improving. I think you mentioned probably one of the most important things and that is being able to play with a more relaxed arm, if you are too tense it makes it hard to play consistent shots. So I would really try to focus on having a relaxed grip which will then allow your arm and body to be more relaxed.
Try to slow down the shots go for spin and consistency and really keep on building up the level of your basic shots and technique. It would be great if you can send us in a short video of you playing some of the basic shots and then we can offer you feedback and coaching points on how you can start improving quicker, I’m sure with some small changes you will start to see the improvements!