it's not a case of pau being underused. he only put up eight shots in the SAS game but that is more of an abnormality than anything else. dude is just struggling, he's exhausted from playing 40+ minutes a night for the first two and a half months of the season that Bynum was out. it's all catching up to him now.
none of his go-to moves in the post are working out for him, and his struggles on offense have been translating to his defensive game where he's been getting eaten up recently. keep in mind there was talk for the first month and a half of the season that pau gasol was the lakers' MVP.