Some advice wanted for senior kitty

My senior kitty Onyx, who is 15, recently (a month ago) had his rear left leg amputated to halt the spread of cancer in the joint. He was previously a very healthy cat, if a bit overweight. He has recovered fairly well from the surgery and is decently mobile. I am a bit concerned about the fact that his fur is not growing back where it was shaved. It is his entire rear left quarter that is bare. He has also started noticeably losing whiskers. He does not appear stressed, in fact he seems more 'kitten like ' than he has been in quite some time. His appetite is good and he plays, and wants constant affection. Two nights ago he was on my lap (as usual) and when he tried to stand to adjust position, he growled. It happened a few times. Later when I tried to put him on the sofa beside me to get up, he growled at me. There haven't been any more instances of it since. I'm just wondering if there is anything I can do to speed the hair up in its growing, I worry that he gets cold as it's a large bald area, and I am concerned about this sudden whisker loss.

I would ask your vet about it.  Is he on a steroid?  I know my kitty is on a low dose of a steroid,  When he had a dental after being on the steroid it took longer for the fur to grow back where he had an IV then it did before.  I haven't noticed him losing whiskers though,

I'm going to call the vet tomorrow, my end of Nova Scotia is experiencing an enormous blizzard right now and every business is closed. He's not on any meds of any kind. I feed him a mix of wet food and dry, he hasn't lost any weight but I worry it could be a deficiency? He's supposed to go to the vet every few months for an X-ray to make sure there is no sign of cancer in his lungs or elsewhere, but maybe an early checkup would be good.

My cat has lost whiskers (her left side only) twice now that I know of. The longer whiskers (the only white ones) went first. They grew back fairly quickly. The first time it happened was when her owner died and was not found for a day or two. The second time was when we introduced a new in-your-face type cat into the house. I assumed it was a stress reaction. She did not lose whiskers during her latest stressful illness, though one grew out with a distinct bend in it. Good luck getting to the vet. Nova Scotia is being walloped!