As regards the word pain being uncountable, which of the following is correct:
I had a severe pain last night.
I had severe pain last night.
The word pain can be both countable and uncountable. In the countable form, it tends to refer to a specific pain in a particular place and time. The uncountable form is used for the general concept.
Pain can be controlled with some types of drug.
I got a pain in my knee when I was running.
The countable form can also be used figuratively to mean an annoying person.
My son is such a pain when he argues about homework.
In your case, you could use pain either countably or uncountably, but if you are referring to a specific pain then the countable form is more likely.