Easy solution that works within 2 mins - ask husband to feed on the breast that is blocked. It really works, don't need any ibuprofen, massage etc. It's a shame GP, midwife, health-advisers are too shy to suggest this easy solution.
With my two children I often suffered blocked ducts (particularly after expressing - because those devices don't effectively pull all the milk from all ducts).
Also when finished breast feeding, there was some left, that blocked.
Hopefully husbands will be happy to help!