Hey there Luke
I think you should ignore the people who believe that you're trying to be someone that you're not, but maybe you could elaborate on that? Do they simply say "you're trying to be someone you're not" or are they a little more precise?
This kind of reminds me of an episode I ent through in middle school. Basically I had dated this guy and since then one of my closest friends made some not-so-nice comments about me having changed and being someone that I wasn't, which was hurtful because I was just being myself, so I totally get how you feel. You have to know that regardless of whether or not these people are being mean out of jealousy or because they actually believe what they are saying, the only person who will ever know you best is you, so trust your own judgement. Ignore them, stick up for yourself. Show them that this is who you are and that you're not going to change for anyone.
As for the self harm, I'm afraid I have no experience with that and so I have no advice to give.
I hope this helps
Skye