Can laxative use (high daily doses of miralax) cause air fluid levels to be in the colon on ct scan?

Doubtful : Air fluid levels in the colon would suggest an obstruction. Assuming you took miralax for constipation, it would be the constipation that led to x Ray findings. By the way, you may need a propulsant, like dulcolax suppository or tabs, in addition to miralax. Afterwards, try eating fiber products more often in your diet or supplementing with bran fibers (Metamucil) or citrucel (non bran bulk agent)