My hubby always reports anything acidic as tasting "bitter", it could be from dissolved CO2 as well.
My recommendation is next time you "test" it, pour a glass and let it sit at room temperature for a while. See if lots of bubbles form on the sides of the glass. If so, then you'll know degassing is your problem... and perhaps agitating a glassful (or bottleful if you're careful!) might "flatten" it by releasing some of the CO2 that might be causing it to taste acidic and sparkling.
And hey, if that doesn't help, you could always cut it with some more nectar when you drink it, then at least you'd have the flavour...
"The main ingredient needed is 'time' followed closely by 'patience'." - The Bishop 2013
"When you consider that laziness and procrastination are the fundamentals of great mead, it is a miracle that the mazer cup happens." Medsen Fey, 2014
"Sure it can be done. I've never heard of it, but I do things I've never heard if all the time. That is the beauty of being a brewer!" - Loveofrose, 2014
"I tend to....um, er, experiment, and go outside the box. Sometimes outside the whole department store." - Ebonhawk, 2014