Looks like there has been a subtle injury
to the eye which has resulted in chemosis and sub-conjunctival hemorrhage. It is better to get the eye examined by an ophthalmologist for a closer look. A sub-conjunctival hemorrhage would subside on its won within 1-2 weeks. For the pain, you can try taking tablet Tylenol
, 500 mg , 1 tablet twice a day for 1-2 days. If the swelling is at the lid margin then it could even be due to a stye
. Warm compresses, for 10 minutes, to be done thrice a day and tylenol would be enough for the moment in that case.