Exercise ball


I'm wondering if I'm doing it wrong? I've been bouncing and moving back and forth and I feel nothing when I do so & nothing after I bounce or move for no less then 40 minutes since I don't feel anything I can keep going longer. I'm not sure my feet or my position is right??

Sorry I've never done any exercise with a ball so I literally have no clue I'm near the end of 39 weeks so I feel like I should feel something when I bounce?