Left eye is red and feels sandy it's uncomfortable. No swollen and not watery. What can it be?

A few options. I assume the vision is unaffected in which case you should see an ophthalmologist right away. Otherwise it could be dryness, allergy, unilateral infection and some other issues as well. Try treating it with over the counter antiallergic drops like Zaditor, and if this does not work then seek help.