Okay so first get the oral swallowing correct, that will be a big help and you’ll find all the videos needed on YT from Thr Orthotropics channel. 

What to do next I think depends on anatomy. From my own experiences, I’ve got a very melted face so to speak, with TMJ, asymmetrical features, and a palette at 31mm when last checked.

So chewing gum for me was not a good thing, and made my jaw worse because it’s so far swung down the joints wear wrong so to speak. 

I pushed up with my tongue focused on the back for a long time (a year) because that’s what I could do, and sleep on my side with a hand to keep my jaw closed. I likely loose a lot of progress because I need an expander at night to keep what I do in day (my body won’t keep my tongue up it’s too squished) 

Next, ive moved my tongue position to go forward and up with some pressure in back - so basically depending on how your anatomy changes and what our working with it’s a little different for everyone! 

Figure out: 1) palette width 2) if you have TMJ 3) can your body Mew at night and by knowing you’ll be able to skip ahead of someone like me who has slow progress (32 years old) and many limitations.

That being said, I’ve seen some great changes even if others are still hard (my profile can literally make my head vanish into my neck with a chin tuck!) But just keep going and you’ll see change over time :) 

About once a week or so I notice that my posture feels noticeably different (usually in a bad sense) in my mouth. Stuff like my tongue isn't having ideal contact or coverage. I imagine the tiny changes over time as you're mewing can really influence how these feelings... feel. If you hadn't done mewing for quite some time it's likely you lost progress and lost skill/habit which is gonna make whatever your most recent successful posture was, feel alien to you.

I genuinely believe that mewing is something you have to learn to evolve and adapt with as your molar distance and palate expand (or shrink in your case). It's very normal I think to feel frustrated when it feels like somethings off. You just need to keep at it until you get it right. I'd suggest you sit down in a quiet place for some time, close your eyes and tuck in your chin so you can focus entirely on regaining control. Ensure that your tongue tip is behind your incisors, supporting that small flat bit behind them and pressed against the slope behind that, as far back into your mouth as you can. If you can do this and block your mouth airway, that's great. If your molar distance is less than 40mm you will likely have to bend your tongue into a ∩ shape to avoid the teeth. This shape is good because it can press into every part of your upper mouth forwards, upwards and laterally. Avoid a  U shape because it doesn't cover the palette as well.

Do you have a tongue tie?

I think not but just to make sure, what do you think?

Also, thank you two for helping! One question tho: How do I measure my palette width? Got no clue. Also, I've seen some conversations about palette expanders, should I get one?

Grab a tailors tape and measure the distance between these two upper molars. It doesn't need to be perfect. Within 1mm of error is fine.

It was about 38mm. My tongue is like 45mm.

That's plenty to start without mechanical expanders. I had about 38mm also and now it's around 40mm. 

My bad, my tongue is actually more like 48mm.