I (stupidly) looked online and Googled this -and i think it's possibly a Basal cell carcinoma. It has not healed in probably 9 months to a year and crusts up after it is scratched but never gets better completely.
Do you think i should go and see someone about this? (I put a plaster on it last night to try and heal it once and for all and i ended up with a plaster-shaped rash on my chest - mmmm, attractive!)