Ihad always been a sickly child, suffering more than my fair share of childhood ailments: asthma, chest infections and flu. Other kids called me a "weaky" because I was skinny and hopeless at sport. I hated rough-and-tumble boys' games and preferred knitting, but I had no idea my feminine leanings were down to genetics.

Then, when I was 13, I collapsed while riding my bike. My immune system was run down and I underwent a series of tests. They diagnosed Klinefelter's syndrome, which means I have three sex chromosomes, XXY, instead of the normal XY for a male, or XX for a female. The condition affects up to one in 1,000 boys – physically I'm male, but genetically I'm male and female.

"You won't be able to have children," the doctor told me nonchalantly. Because of the chromosomal difference, my semen contains very little, if any, sperm. Even as a teenage boy, I was devastated and burst into tears. I'd never even kissed a girl, but I'd always wanted children. I was put on testosterone injections to induce puberty – to help turn me into a man.

I don't remember my parents ever discussing my diagnosis. Perhaps they were too shocked. My dad muttered something about still being able to adopt, and didn't return to the subject. The only person I told was a priest who offered to pray for me, but it wasn't prayers I needed. I wanted emotional support. I felt isolated and confused.

Then, a year after my diagnosis, my sister Teresa was told she had cervical cancer. She died a year later, aged 30, before I had a chance to confide in her. Soon afterwards, my mum was also diagnosed with cancer and died when I was 21. Cancer deprived me of the two women I loved most. My own condition seemed negligible in comparison.

I moved to Segovia in Spain, my dad's home town. I spoke the language, so it was easy to get work. The rest of the time I spent partying, and DJing, anything to dull my sense of loss. I also lost my virginity – it was a hazy, forgettable event, but I remember thinking: "I'm a man now." I was 24, but looked barely old enough to smoke. I'd neglected my testosterone injections because I couldn't get a prescription there.

Two years later, I came back to England and began to face up to my condition, resuming the injections. I became heavier. Hairs sprouted on my chest. At 25, I had my first shave, my hand shaking with excitement.

Physically, I began to look masculine. But inside I felt feminine – and I still do. It's not that I want a sex change and I'm not gay. I just enjoy the things other women enjoy. I love shopping and trying on clothes. If I'm going out, I'll spend ages getting ready. I loathe Top Gear; I'm not interested in cars or football. I'd rather watch Desperate Housewives with a glass of pinot and a face mask.

I'm sensitive and emotional, but every three months I have my testosterone injections, which take 48 hours to kick in. Suddenly I feel like a "man". It starts with a stinging sensation in my legs, followed by a horrible restlessness and anxiety. Then I want sex and feel irrepressibly drawn towards anyone with breasts. If I'm lucky, I'll get a one-night stand. Fortunately the effect wears off after a day or so.

One of the worst things about Klinefelter's is it can make me depressed and insecure. Another problem is I have little sex drive (except after an injection). This makes relationships difficult and I've had few girlfriends. Although I'm physically capable of sex, I often freeze up. It makes girls think I'm either gay or don't fancy them.

So when I met someone online, I decided to be upfront about my condition. I was amazed when she told me it didn't make a difference and we've been together for three months now – my longest relationship. It helps that she's a nurse and is naturally caring. I still feel broody but my girlfriend has two children of her own which feels like the ready-made family I never thought I'd find.

I feel so fortunate to have met someone who accepts me the way I am. There's no cure for Klinefelter's, but given the choice I don't know if I'd change it. I'm sensitive, creative and artistic, and perhaps that comes from my extra X chromosome. I try to see it as a bonus, rather than surplus to requirements. I guess you could say I'm just very in touch with my feminine side.

• As told to Becky Dickinson.

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