Hi i had a total hysterectomy 23 weeks ago and from day 1 iv had an protruting stomach?

thats very hard to the touch. when i sit or lay down its a typical jelly belly but only when i stand does it get very hard. im in no pain at all and my bowels and pee are normal.however iv gone back to my GP because people keep saying that doesnt look right you look 6month pregnant as iv done since i had it done. My GP said straight away theres something wrong there he examined me and couldnt feel any lumps or bumps etc he did however say it could possibly be fluid and iv to have a scan in 3 days time. what id like to know if anyones any idea is if its fluid why would all my tummy swell? and any other ideas what he thinks could have gone wrong i feel perfectly well in myself. thanks