[tamersalama]

That device is represented in every phone and tablet. It just needs the software to capture it.

[jacalata]

It doesn't even need to be real-time. An app/text message that asks you every three hours "been cramping up lately?: No, once or twice, several times, lots"* would collect a lot of relatively accurate information, and easily show you 'whoa, I cramped up almost every hour this week, two months ago it was once a day!'

*in my answers I'm assuming that we are tracking the incidence count, rather than duration/severity - this is easily adapted if necessary.