Had a rootcanal last year if the infected root wasn't takin out completely could the infection give me pressure in the side of my head who do i go to?

Dentist/endodontist: If you're worried that your root canaled tooth is the cause of your symptoms, then go in to see a dentist or an endodontist.

Dentist\Endodontist : See an endodontist to evaluate the tooth. It's the nerve and tissues inside the root(s) that are removed and then the canal(s) are filled; not the roots themselves. Your symptoms may or may not be related to that tooth and may or may not be related to the success or failure of the rct. See your dentist to determine whether or not you have any dental problems, or unrelated medical symptoms.

Dentist: If you think that the root canal treatment you got is the reason for the symptoms, then you should see a dentist to determine if that is the cause and what to do about it, wether by re treatment of extraction or other treatment options.

Have tooth checked: Go back to your dentist and have your root canal treated tooth checked. Pressure or "fullness" in one side of the head could be a symptom of many pathological processes. Sinus infections is one one of them. Also, if root canal treated teeth are not restored, meaning do not have a crown (cap) or at least a good filling (while waiting to be capped), they tend to reinfect, fracture or both.