Why dard ho raha?
There is no commonly used verb that is equivalent to 'to pain'/'to ache' in Hindi.
दर्द is a noun. So, taken literally, the Hindi sentence 'मेरे कान में दर्द हो रहा है' would translate to something like ' Pain is happening in my ear'.
Thank you so much. I fully understand your explanations.
Why मेरे and not मेरा/मेरो if it is about a single कान?
The noun phrase 'मेरा कान' is in the oblique case due to the postposition में. The oblique-case form of मेरा is मेरे and of कान is कान itself.
Would the plural oblique case be कानों?
मेरे कान में = in my ear, दर्द हो रहा है = pain is happening.