This app was mentioned in 6 comments, with an average of 1.33 upvotes
I've been using "med helper" to record my painkiller usage. https://play.google.com/store/apps/details?id=com.earthflare.android.medhelper.lite&hl=en_GB
Little fiddly to setup but nice and simple once you get going.
This app does the job
https://play.google.com/store/apps/details?id=com.earthflare.android.medhelper.lite