I am so sorry you are having to deal with this on top of everything else. I had shingles, and it was -- and still is on occasion -- brutal. I still feel it now, and I had the rash 2+ years ago.
I asked my doc about getting the shot after the rash healed, and he said that it wouldn't have eliminated the chances of getting shingles but it might have lessened the severity. I am pretty sure I also remember him saying that once you've had shingles, the shot was mostly moot, but maybe I made that up in my brain. I have no clue whether a person on chemo could get the shot or not so sorry I can't help there. I think the concern for those with compromised immune systems is if the vaccine contains a live virus.
The best advice I can give you is to let go of the stress, as post-herpetic neuralgia is pretty horrid and much more likely if you/your body is stressed. Easier said than done, I know.
-snapfish
Daughter to 70-year old father dx 2015-Sept-28: Stage IV adenocarcinoma with signet ring cell features
Sigmoid colon primary with peri mets
MSS; RAS wild-type; mutation in exon 8 of p53
2015-Oct: Began FOLFOX-6 at MDA; CEA was 15.1 at baseline
2016-Feb: CEA 5.7; 10 full rounds of FOLFOX-6 completed
2016-Mar-3: Began FOLFIRI
chemo, chemo, chemo
2017-Jan: Total of 29 cycles of chemo down. Back on FOLFOX again after FOLFIRI fail. CEA now 118.