I think I'm finally getting the back of my tongue up there in the right place.
Just a few questions: Is it normal that when starting placing tongue on the roof of the mouth (I mean especially the back third) to get a vomiting reflex after a few seconds of a try? And will this just go away when you get used to it?
And the times I don't get that vomiting reflex, my tongue will get exhausted after like 10-15 seconds like I was working out a muscle. Are these just normal things in the beginning or am I doing something wrong?
Not easy to determine what is normal and what is not, but I can see that happening. Try to find a sustainable balance between effort and inconvenience.. In small mouths the pushing doesn't have to (and can't) be perfect. Expansion to any direction is a big victory and will make things many times easier. Muscles will adapt quickly.
One thing you can try is to place something thin on your tongue and push up against that. Like a small piece of paper, or a piece of gum wrapper, or a mint leaf or something. Whatever you have handy, it's not very important what it is, just that it is thin but that you can feel it there. I find that pushing up against something is much easier for the muscles to understand than simply pushing up against the palate.
Give that a try and see if it doesn't help you feel things more clearly.
Also about you having a tongue tie or not, I've seen way worse and it doesn't look like you have one - but I can't be sure from that picture alone. Check out this video at the specified time and do the self-test.
https://youtu.be/HwZ0YhQXlN0?t=728
During the rare times when I get the correct posture and know that it's exactly right, I have gotten the vomiting reflex most times. Of course, I'll then try to adjust my tongue and thus lose the posture, so keep at it and see if the sensation goes away.