What I'm doing next ... taking a lot of medication (9)
I believe the answer is:
compiling
'what i'm' is the definition.
I can't judge whether this defines the answer.
'doing next taking a lot of medication' is the wordplay.
'doing next' becomes 'coming' ('come' can be a synonym of 'do'. I am not sure about the 'next' bit.).
'taking' indicates putting letters inside.
'a lot of' means to remove the last letter (a lot of but not all of the word).
'medication' becomes 'pill' (pill is a kind of medication).
'pill' with its final letter taken off is 'pil'.
'coming' enclosing 'pil' is 'COMPILING'.
Can you help me to learn more?
(Another definition for compiling that I've seen is " Creating a collection".)