Seems like he might be having some gas troubles.
You do not want to forcefeed when there is a blockage, so see here for guidance on how to try identifying it at home: https://www.youtube.com/watch?v=iVW6Rw5rZzo
If it is just gas pain with no blockage, some at-home treatment can be effective in helping him get through it. If it is approach several hours of no eating (~12), it is an emergency and he needs to see a rabbit-experienced vet. Also, if there is a blockage, veterinary intervention is needed immediately. See here for some at-home treatment and things to monitor related to GI stasis/distress: https://wabbitwiki.com/wiki/Gastrointestinal_stasis#At-home_treatment
Main things to keep in mind are when your rabbit last ate and pooped, encouraging movement (to help gas), using simethicone (to help gas), and keeping your rabbit warm (if getting cold).
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.