I actually built a simple one (also for Android) as there wasn't anything easy out there.
One thing that my gf wanted as additional features was the possibility to also track mood (I let her choose among 5 ranges of emojis) and add tags to each day: for example she can create a tag "pains" and set if she had cramps a day or not. All that can be expected to csv/xslx for her own analysis.
If you add these features, I'll recommend this app to her instead :)
Also my app has a minimum SDK 20, so it works with her ancient phone.
One thing that my gf wanted as additional features was the possibility to also track mood (I let her choose among 5 ranges of emojis) and add tags to each day: for example she can create a tag "pains" and set if she had cramps a day or not. All that can be expected to csv/xslx for her own analysis.
If you add these features, I'll recommend this app to her instead :)
Also my app has a minimum SDK 20, so it works with her ancient phone.