Me duele…
Aches use doler, with the part that hurts as the subject: me duele la garganta, me duelen las muelas. La muela is a back tooth, but a toothache is usually dolor de muelas, whichever tooth it is.
La oreja or el oído?
La oreja is the outer ear, the part you can see. El oído is the inside of the ear and also the sense of hearing, so an earache is normally dolor de oído, and a musical person tiene buen oído.
At the pharmacy
Expect advice with deberías and podrías (debería and podría with usted).
In Spain, antibiotics need a prescription, una receta (the same word as a recipe), and they do nothing against a virus (plural los virus).
To book the doctor or the dentist, you pedir hora (or pedir cita).
Marear and marearse
With marear, what makes you dizzy is the subject: el barco me marea. With marearse, you are: me mareo en el barco. In everyday speech, ¡No me marees! means stop pestering me! or you're making my head spin!, said to someone who wears you out with talk, questions or changes of plan.
Izquierdo and el codo
It agrees like any adjective: el codo izquierdo, la mano izquierda. And someone who never stops talking habla por los codos.
