This will probably be a bit rambly but here is a little background. I'm 16, and have Anxiety, OCD, ADHD, and High functioning Autism. As far as I remember I actually grew up with proper (or alright) oral posture, it wasn't until I was around 13 when I started mouth breathing. I have seasonal allergies and one spring I guess it was worse than normal, because my nose was completely stuffed up which forced me to mouth breath. And I never stopped, even when my nose cleared up it continued, it had become a habit, one that I have been trying to break for almost 4 years now with no luck. I'm not sure if my disorders and hyper fixation are part are part of the reason I'm unable to correct the habit but I wouldn't be surprised. So yeah probably less than a year after I had started mouth breathing I realized it was a problem and started trying to fix it, I did research and read that you should have your tongue of the roof of your mouth so I tried that, for years trying different placements and positions but I just couldn't get it right. It was only a couple weeks ago that I found out what mewing was and that there was a whole community around it, and I decided I wanted to get serious and fix this once and for all before my facial structure deteriorates more and I run out of youth to moldablility. I actually didn't even realize that my jaw had receded until I took profile shots, because from the front and in a mirror my jaw shape actually looks pretty good. I think that this might be because I grew up with proper posture so my jaw developed decent but has sunken in since I started mouth breathing. I have also noticed my cheeks and lower corners of my face "sag" downwards, almost like a bulldog, which wasn't the case when I was younger. What I was thinking is that maybe since my jaw and face developed well, and I only adopted incorrect posture later in my childhood, my face has started to grow down, but since my bones didn't grow that way it has made it sag and droop. I do have a question, when I have my mouth in the proper posture with my lips relaxed, they do not seal at all, which is an important part of mewing. Should I leave them relaxed and open or use my muscles to hold them closed. One thought that I had is that it could be related to the whole saggy face thing. if my lower face is started to droop downwards, maybe my lower lip has pulled down, away from my upper face. I could be completely wrong on everything, these are just some possible ideas I had.

Sorry for the wall of text, any help is appreciated! Also if you see anything else I should work on let me know.

(I've included a Google Photos link, if that's not allowed I can upload them to somewhere better)

https://photos.app.goo.gl/15wd4Key9Ki44ci36