I’m sitting in a coffee shop in LA when my friend Lou says, “Give me your phone and I’ll download an app that tracks your menstrual cycle,” like we’re suddenly starring in a uniquely naff advert for solipsism in the 21st century.

I look around in case anyone has heard us. “Why on earth would I want that”, I mutter to her. My period comes fairly regularly, then it goes away again, and I’m not trying for a baby, and all right, so the whole thing does actually take me by complete surprise every single month, because my head and the clouds have always been in quite close contact – but still. I don’t really feel the need to inform my phone when I’ve got the painters in.

“What’s your password?” she says, getting me something called Hormone Horoscope Pro regardless, and charging a couple of quid to my account. That was two months ago, when I was on holiday – and I’ve stopped being sarcastic about it now. Honestly, back in my real life in the UK, I can happily declare that hormones are an utter revelation.

Firstly, this app – and there are others like it – is nothing to do with astrology. It is everything to do with making you realise that, if you’re someone who menstruates, then you are always, at every minute of every day, experiencing some part of that cycle. It’s not superstition, it’s biology.

This hormonal journey doesn’t just affect fertility – it affects your courage, your self-worth, your attractiveness to others and your energy levels, and the idea is that you can use the knowledge to plan your life accordingly. The first day of your cycle is the first day of your period, and then after that you can track everything.

Well guess what – it turns out my ever-changing personality actually makes total sense. I’m not actually a moodswinging weirdo who wants to run up to strangers singing naked hosannas to the moon and the stars one week, and then stay in my room focused solely on death the next – I mean, I am, but it all clicks into place now. I’ve just been going through the various stages of my cycle, and feeling the lovely rush of oestrogen, (which drops twice every cycle), or the onslaught of progesterone, without realising I could work with them rather than against them.

Ovulation! I’ve learned so much about how ovulation affects my social life! Honestly, please invite me over to your house at this time, and not just because my body is programmed to try and have unprotected sex with you. My desire to be around other people is at its zenith. My social nerves disappear. My jokes are funnier. (No, I’m not ovulating while writing this column, how could you tell ... ?)

As someone writing a book, I also see now that the boundless ideas and juicy flow of words all come in the first half of my cycle. The quieter time for reflection, perhaps casting more of a critical, doubting eye over the material, comes in the second. I mean, it’s clear to me now that Elsa from Frozen’s real problem is that she spends her entire life in the second half of her cycle. It’s not depression – it’s progesterone.

I spoke to Maisie Hill, an acupuncturist and doula who has been studying menstrual cycles for some time. She says she tries to organise any public speaking engagements for day 12, what she calls the “Oh hello world!” time, when she knows she’ll have the most confidence.

It’s not just women. I also spoke to the US publisher David Shook, who admits he spent years confounded by a low sex drive, bouts of depression and weight gain, before finally discovering that a teenage head injury, long forgotten about, had damaged his pituitary gland. So his body could go through the motions but the instructions to do so weren’t there – because, when he finally got them tested, it turned out he had the testosterone levels of a 90-year-old man. Now he injects a variety of hormone treatments into his body every morning – extremely similar to what he would be taking if he were transitioning from female to male in gender reassignment – and life has changed immeasurably.

I emailed someone about my hormone revelation and it got lost in their spam filter – it seems all the mention of hormones puts you straight into the murky underworld of black-market drugs. And perhaps that’s what hormones are – the drug dealers in our midst; the naggers, the tricksters, the cheats, alternately cock-blocking and randy, pushing you forwards, holding you back. At some points of the month they are like Mrs Bennet in Pride and Prejudice, shoving all her daughters in the face of suitors.

At other times, they are the parent who says children should be seen and not heard, and who won’t let you speak in public lest you bring shame upon the family.

For me, the most exciting thing has been learning to listen to what they’ve been whispering at me all this time. And to apologise to my friend Lou – you’re right mate, it was £1.99 well spent.