I had the same worry at that time myself, my doc ran an ultrsound just to ease my mind and found the placenta right on top of my stomach and the baby is also breech.. She told my that they don't really worry too much about movements until around 28 weeks, then she wants me to do "kick counts".. She said at 24 weeks the baby is still pretty small and that I shouldn't worry... Hope this helps!
I'm sure this is very normal, so try not to worry. They are constantly moving and changing positions all the time, and maybe he is just so nestled and cozy in a certain position that his movements aren't as prominant. I can understand why you would worry, I was the same way, although my little guy moved around alot from 18wks on. But some days I would only feel one or two movements, then nothing the rest of the day. Other days he was doing gymnastics all day/night long. I doubt your gastro virus has anything to do with little or no movement. Are you drinking lot's of water? I have always gotten a movement response after I had something to drink. Wow, you're almost 25 wks, really getting up there, you're over 1/2 way done!! I'm sure all is fine, but of course contact your doctor if you don't feel any movement in the next couple days.