Highly recommend
I have been using this app since October 2013 and I’m very happy with it. It’s very reliable (although my period is not) and lets you record a variety of data including any symptoms, feelings, notes you might like to keep. The user interface is nice and clean and modern. When I changed phones in 2017, I was able to backup my data and restore it on my new phone without hassle and that was great. My only qualm is that the app lacks a connection with the Apple Health app.