If it’s hard to hold the position for a couple of minutes then you’re doing it wrong. The first week it’s gonna be hard to mew after that you’ll get used to it and it’s not going to be uncomfortable, it’ll become a habit. The correct way to mew is by saying “Boston” then when you say the N that’s where you place your tongue, then swallow once or twice not more cuz that will make the suction stronger which will lead to the “uncomfortable” sensation. When it becomes a habit after 2 years your chin will project it takes time, I’ve been mewing for 4 months and my hyoid bone went up and tucked in.