I'm not on Keyruda, however I experienced symptoms like you describe in addition to a weird sensation of muscle twitches traveling up and down and around in my legs. I took gabapentin which helped with that, but it didn't help with bone pain and muscle stiffness or peripheral neuropathy. For these symptoms I took ibuprofen, which helped somewhat. I also tried to move my body, walking especially, helped. When the pan eased I I resumed Jazzercize-- the dancing really helped.
The pain does ease after after the first week after treatment; and while the neuropathy lessens it doesn't completely disappear.
Try to keep moving and remaining positive.