If this is interesting to you, you may also be interested to check out the book The Light Eaters by Zoe Schlanger

I personally try to steer clear of diphenhydramine for anything other than one off purposes just due to the research coming out regarding anticholinergics and possible cognitive decline. It sounds like you’re taking it relatively infrequently, so I’d guess that’s ok. Just linking here for others for visibility as it seems like perhaps not the best long term solution.

https://www.health.harvard.edu/blog/common-anticholinergic-drugs-like-benadryl-linked-increased-dementia-risk-201501287667