Submarine Grips

I am 16 years old and entering junior year in high school, I play 2nd base and just started pitching. I have been throwing submarine bullpens for a while now and just got the oppurtunity to throw it in a game. I did quite well and gave up no hits or walks in two innings with two strikeouts. I throw a fastball in the high 70’s with good control (still working on that). I also throw a changeup (circle change grip). I do have a few questions though that I hope some of you can answer. I do not throw sidearm, i throw submarine, not as low as chad bradford but it’s down there.

  1. When throwing submarine i consistantly throw from a 1/4 armslot, but sometimes my pitch dives back down and in to right handed hitters (I am a righty), but sometimes it doesnt really have any movement. I throw this with a two seam grip and change nothing, does anyone know why this is?
  2. I need another pitch besides fastball curveball, what are some diffrent grips that I can try?