yeah, energizer can definitely leave a little after taste in mead if you use too much, or if its not utilized.
you are not too late in fermentation, but I'd only add a small amount, gently stir it in, and call it good.
I've had meads turn out without using any energizer/nitrogen. It just takes a while. You definitely don't wanna rack it too early. Stir up the lees when you dose the energizer, then let it settle back down.
a month in primary is ok. you won't get off flavors (autolysis) in one month.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10