From what you describe it sounds like an inflammation of the sclera or white part of the eye called episcleritis
. This is common in persons with some connective tissue
disorder or rheumatoid arthritis
but can happen without obvious cause. Antiinflammatory eye drops a few times a day works along with lubricating eye drops. If this returns so often you may need to visit an ophthalmologist for confirmation and a few blood tests to rule out systemic disease.