I would see an optician. They generally know more about eyes than doctors do. Some of them have a sign that says NHS red spot. The NHS are trying to reduce the use of antibiotics for eyes, and doctors usually just give antibiotics, whereas an optician may know of another treatment.
When I had a very sore eye, also felt as if there was something in just one spot, the optician looked inside my eyelid and found a small pimple. he recommended Optrex (what he called 'artificial tears') and told me to gently rub my eyelid at the sore spot to help the pimple to disperse. And it worked!