I’m counting down – that’s how I work each marathon. I’m more than halfway through my 27 marathons in 27 days challenge through South Africa for Sport Relief – 27 days to mark the number of years Nelson Mandela spent in prison. My final marathon ends in Pretoria, South Africa, on the steps of the Union Buildings where he was sworn in as president. I’m knackered and both legs hurt to varying degrees. I run each day until I’m done, which takes about seven hours. I don’t listen to music because the cars go really fast here – I don’t want to get hit. I link in to what’s around me – buffalo, tortoises and turtles, wildebeest, ostrich, zebra. If you’re listening to some band, it cuts out a whole bunch of senses.

It’s tough fighting boredom; when I get very hot and tired, my brain doesn’t work right. If you’re morose, you won’t finish the run. I sometimes mutter to myself or sing. I like singing the theme tune – a Mozart concerto – from Out of Africa. I’ll witter to myself on occasion, too. You have to keep your mind happy to make sure the dopamine is flying around the brain.

How do I prepare? It’s about building confidence. I wasn’t very good at the start, but I gradually got stronger. That’s what human beings do. I’m quite ordinary like that, but my determination is good.

I came out as transgender 30 years ago and that was tricky to do. It sounds bizarre but, ever since that point, I’ve been able to do quite difficult things. Walking out of the door wearing heels and makeup was so hard. I had to get my brain ready to do that. But it prepared me for everything else difficult that I’ve ever done in my life.

My only advice if you want to run a marathon is: listen to your body. We’re animals, but we’ve stopped listening to ourselves, so if something is aching stop pushing against the muscle; if you want to keep going, then walk it out or change the way you’re running. But listen to the signals.

I’m aware of my health this time around. In 2012, I came here and attempted this challenge but had to stop after four marathons in four days. After the third, my pee turned brown. We discovered it was a reaction to the medication I was taking for my cholesterol. The heat was pretty bad, too.

This time, on day five, I was told to rest – we couldn’t tell if the problem was heat exhaustion or my kidneys. I went to two hospitals and the specialist said I was fine, but that I needed to keep my hydration up. I fell a day behind, which means I’ll have to run two marathons on the last day, it’s called the Comrades Marathon – 56 miles in a day is what I’m going to attempt.

Still, I haven’t been this healthy since I was a kid: I eat porridge with honey for breakfast, boiled eggs, then banana, dried mango, and at night I eat salad, meat and fish to rebuild muscle.

Running has changed me – seven years ago, I ran 43 marathons in 52 days for Sport Relief around the UK. I’m a different person now. I’m the child that I once was – running around and climbing trees. I can look around and say: “Hey, look, there are some mountains over there. Let’s run over to them.” It’s kind of crazy but that’s how I feel running around. I’m 54, so if I can do 26 miles every day, anyone can.

•Follow Eddie’s journey at BBC3 online and donate or sign up to the Sainsbury’s Sport Relief Games