Hi Andre, a very warm welcome to the community. Nice to read your log. Reminds me of my early days of playing…
A lot of fellow students had or have the same issue and you can find several threads concerning posture and ways to hold the guitar, e.g.
How To Hold Your Guitar
Maybe worth a look, to find some helpful ideas. It takes some time to find the right position for oneself, as everyone is different and every type of guitar is different. Time will tell. And you can always ask, when your problems persists.
Wish you a lot of fun with your guitar playing!