I think my mice are in pain please help?

im really scared for my mice, they drink a lot of water and i think theyhave t run on the wheel in order to not be in pain. I was holdin Daisy (Daisy and Ruby are new to th famiy and im esp taken a bond w Daisy) she was rly startin to trust me and out of nowere shes standin still and her lower body was makin weird movements. and theyr always runnin and so desperate they run together, i gta geta bigger 1. theyr lower abdomens seem to protrude, and they sniff eacothers a lot. i considered pregnantand they make weird movbemebts when not movin around this is killin me. whats wrong?? how can i help? whats causing this? i hate to see animals hurting and i cant do anything about it. im cleanin the tank now and use that cardbard ish bedding, not teh wood shavins but this fluffy 1 they use in some petstores. could it be the bedding? called carefresh natural. scared help! they jus pooped very runny and diarhea 1 did at least and they pood 2x VERY weird im cleanin the tank now---ok jus cleaned it mae a special healhy water.