Hi Lissy, in my experience there could be a couple of reasons why Oreo is quiet.
Firstly he is still very young are still settling in his new home, and then secondly rabbits can and do grieve for the loss of a fellow bunny friend.
Make sure that Oreo is eating, drinking, weeing and pooing normally those things are most important. Give him time to settle down and let him learn to trust you and don't forget if you need me personally I'm not far away. x
Try sitting with him and letting him come to you on his own accord. Everything must be done on his terms. Patience by us humans does usually pay off. Just give him time.
If in any doubt about his health, a checkup at the vets would be best.