Headache top right side of head for 3 days after having cavity on left side of mouth filled. Now, my right eye is bloodshot. Throbbing. Help!

Go to your doctor. This could a sinusitis, inflammation and infection of the sinus cavity (maxillary sinus) that makes up the floor of the bony orbit that holds your eye. You need to go to your doctor or the er especially if tis getting worse and/or you have a fever. It could just be refered pain as well. Better be safe and get it checked out.
See doctor. You need to see your dentist, pcp, or ophthalmologist. Difficult to tell what it is. Could just be inflammation. Concern is infection or something unrelated to dental work.

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