Hmmmm, okay so if it is in sparring say "ease it down" and if they don't they are a dick and you should say "you're a dick" then walk away.
But as for holding the pads, that's a tough one cause I know if I'm wanting to train and my partner told me not to hit the pads so hard I would be pretty annoyed. Which I know isn't your fault cause of your naturally small frame but I am there to train.
I would definitely say you need to work out, I don't mean get massive but definitely get some armor on so you stop getting hurt. You seem pretty keen and dedicated which is awesome so it shouldn't be a problem if you can keep motivated, talk to your coaches for sure and see if they can get you on a strength course and sort you out a proper eating plan to get strong.
Best of luck, let us know how you get on.