Less pellets, more hay. They should have hay all day to eat. Pellets are designed to put weight on. They need about half of what you think they need if you are feeding properly.
Vegetables should be fed daily also. Dark lettuces, NO ICEBERG, parsley, celery (remove strings or chop in small pieces), green peppers, tomatoes (no stems or leaves) just to name a few.
Go to
www.rabbit.org for a complete list of what vegs to feed and WHAT NOT to feed.
Then let him/her out to run and play daily. Mine have a huge outdoor pen, they can run, climb and dig to their hearts content. They are in excellent shape, and they are old bunnies.
Check out that website for care info, it is very good.
Oh yeah, easy on the treats, carrots should be given in VERY small amounts, mine get the equivalent of one of the baby carrots per day, that's it.