I dont think your reasons are selfish Mel! Mostly they are things that can be worked around...the gym and BB meet ups will still be there after another baby
The pain thing is probably a big one. You seemed really in a lot of pain with Eden and will that effect your other kids? But again that's a short term thing (in the scheme of things) and can be managed.
Its a tough one but I think you do a great job with the 3 of them why not share some more love!!!!