It could be many things. I use this idiom too. I don't know what I'm doing. https://en.wiktionary.org/wiki/I_mean https://en.wiktionary.org/wiki/I_mean Expres

It could be many things. I use this idiom too. I don't know what I'm doing. https://en.wiktionary.org/wiki/I_mean https://en.wiktionary.org/wiki/I_mean Expressing uncertainty, most likely.