Our bunny wont stop hiding

Recently my bf got the bunny his parents owned (they neglected him a little, only small spaces, no toys etc.) He's been in my bf's apartment for 3 weeks now but the last 3 days he has been hiding under the couch and only ever comes out to eat or to go in his little house on the balkony. We got toys and other hiding spots for him, I even brought him with me home so he can run around in my garden 2 times already because it's large and has lots of plants he can eat and hide under. He was pretty energetic after that, much more then with my bf's parents but now he stopped and sits under the couch all day. Last night he even stomped while he was under there. Does anybody know what it could be? We both have very little experience with bunnies but we are trying our best to give him a good life with us. And if you have any other tips please also mention them, we'd be very happy.