I've finally discovered what the problem was. Seriously, I had latterly been talking to my hubby about seeing a specialist because it was getting so bad.
At first I thought it was grapeseed oil because the itchiness coincided with the first time I used it. Then I thought it may be a food allergy but I couldn't figure out what precisely. Then I went home to my country Malawi and noticed that my scalp wasn't itching and at this point I thought the British weather was the culprit, I began contemplating buying a one-way ticket back to the Warm Heart of Africa!
It's a small tragedy that led to the discovery of the real culprit: our bathtub started leaking so upon our return we started using our separate shower and this shower doesn't have a water filter.
Two weeks into our return I realized the itching hadn't returned and the only thing that was different is that I wasn't using the shower hose with a filter - so the filter was it! One of the chemicals in the filter must make my scalp itch but it normally happens a few days after my wash, probably when the power of the peppermint essential oil that I add to my conditioner wears off!
If you have an itchy scalp and you use a shower filter try not using it for a month to see whether it's the problem. Keep in mind that it may not be; just because I'm allergic to something in my shower filter it doesn't mean you'll be!