I'm 36, and last night in bed my boyfriend pointed out my left nipple has suddenly started turning inwards. Does this matter?

Inturning of the nipple can indicate serious trouble in the breast. You really must see your GP this week and ask her to refer you to the local Breast Unit for assessment. However, in order to avoid frightening other readers, can I just stress that when a woman's nipple has been inturned all her life, that's a different matter and does not indicate serious disease.