虫歯が痛いですって英語でなんて言うの？

In general, the exact location and type of tooth problem is not important here. You just want to express that your teeth are causing you discomfort. This is usually encompassed within the phrase: "I've got toothache!" You could say, alternatively," Ouch! I need a filling!" when the pain hits you. Or you could say, "My teeth are giving me gyp!"
Gyp is a moderately common expression, mainly in the UK, but also in Commonwealth countries. It appears in fixed phrases that refer to some part of the body being painful, as in this example from the London Evening Standard in August 2003: “I turned my ankle in the game and it’s still giving me gyp..”

"I've got a bad toothache." is a general statement to describe that a toothache hurts very much. When we use the term "killing me" its used as an exaggeration to express how bad the pain is.

In the first statement, you are using the adjective 'painful' indicating that you are experiencing pain because in your tooth because it has a cavity.

In the second statement, you are using the verb 'hurting' in the present continuous tense because the pain is not stopping due to the cavity.

In the third statement, you are using the noun 'toothache' to indicate that one of your teeth is aching, and then specifying the cause of the ache, which is the cavity.

Dental pain or tooth-ache is a really painful experience...One that most of us will go through at least once in our lifetime...This is cause when the nerve or" pulp " of the tooth is infected or exposed. We need would need to seek a dentist ASAP!
"I was suffering terribly with a tooth-ache untill I got to my dental appointment..."

When you have a tooth with a cavity and it hurts, then you can call that a "toothache".
For example, you can say:
-I have a cavity and it's aching/sore.
-I have a toothache.
-I need to have my tooth taken out. It has a cavity and it's aching.