That sounds normal, don't worry it doesn't last foreer. I used to struggle getting through 4 hour shifts when I was younger without feeling stir crazy. Now I'm in my 30s and 10 hr shifts fly by in comparison. Two big things happen, as you keep getting older your perception of time passing speeds up, and as you get more responsibility you'll feel more invested in what you're doing.
That being said, you will eventually outgrow your job and need more of a challenge. I don't recommend staying at a job where you aren't developing anymore.