Update: I swung past the optician yesterday to get my eye checked.
They suspect iritis and I'm seeing the ophthalmologist at the hospital tomorrow at midday! My eye has got quite red and inflamed too over the last few days. Hopefully it can be sorted quickly.
A bad case of iritis.
4 different types of drops and an appointment for next week to monitor the medications, plus a stern warning never to leave it this long and to next time just go straight to the optician's.