I don't think the arm angle matters all that much---remember Orlando (El Duque) Hernandez, who used several different ones. But you have to be able to throw all your pitches, regardless of arm angle, with the same arm speed and the same arm motion, and it seems to me as I read your post that you haven't been doing that. No wonder the batters have been picking up on your stuff! So I would suggest that you work on this aspect of pitching, maybe with the help of a good pitching coach.
I remember when I was playing, many moons ago, and we were facing a team with a starting pitcher who had a beautiful slow curve---one of the prettiest I had ever seen---but the stupid was telegraphing it! He would twitch his elbow in a peculiar way when he was going to throw it, and worse yet, he slowed down his arm speed---a no-no in any pitcher's book. We picked up on that immediately and knocked him out of the box in the early innings, without fail. So you need to avoid that.