Green’s Dictionary of Slang

to annoy, to upset.

1988		A. Payne ‘The Last Video Show’ Minder [TV script] 39: Listen, you wanted to know what was agging me, so I told you.
1997–2001		Online Sl. Dict. 🌐 ag [...] v 1. to pester, irritate, annoy. Origin: possibly from the word ‘agitate.’ (‘She ags everybody.’).
2007		L. von Amerongen Teen Talk n.p.: She really ags me.