In Spanish (or at least in Argentina), when we are receiving medical attention we say the doctor is "treating" us (tratando) . "Estoy recibiendo tratamiento" (I'm receiving medical attention). This doesn't sound very natural in English (saying a doctor is treating me for receiving medical attention). How do you express the same idea in the most natural way in English?
To receive medical attention and to receive treatment are perfectly valid phrases, though they sound a little formal and are the type of phrase you'd see in news reports or on hospital forms.
More informally, we often use be treated for [something] or even say where this treatment is happening, such as be in hospital for [procedure/illness] or go to the doctor's for [illness].
Another informal alternative is that you say what actually happened when you sought treatment, such as the doctor gave me some medicine for [illness].
In addition to Dan's excellent answer, a common expression is "to go to the [doctor / clinic / hospital / emergency room] ..." Examples:
I went to the doctor yesterday to have him look at this bump on my neck.
I took my mother to the emergency room because she was having trouble breathing.
My wife went to the clinic to get a flu shot.
If you are referring to treatment that consists of multiple treatments over time it is common to say "I am under the care of Dr. Goodman." or "I am Dr. Goodman's patient."
A patient is: "A person under a physician's care for a particular disease or condition." http://www.medicinenet.com/script/main/art.asp?articlekey=39154