Hello,welcome to HCM.
Considering your previous
injury was 9 yrs ago ,I do not think that will cause pain now.
Since your pain is occasional and only in one eye,few more questions to assess your condition.
1.Any discharge/crusty lids when you wake up?-it could be due to blepahritis/early
stye , which needs regular warm compresses and an antibiotic eye ointment therapy for atleast 2 weeks.
2.Any associated redness/burning sensation- suggestive of Dry eye-which is usually seen affecting both eyes.Any of the over-the-counter Lubricant eye drops-4 to 6 times a day for 2-3 weeks should give you temporary relief.
Apart from these mentioned above,an inflammation of the inner structures of your eye also could give you a vague intermittent pain.Keep a watch on your vision and light sensitivity.
So I would suggest you to try Lubricant drops for a week and have a direct eye exam just to make sure your vision and rest of the structures are with in normal limits.The remedy depends on what you get diagnosed with.
Hope this answers your query.