The singer claims he's been officially diagnosed with schizophrenia and bipolar disorder, manic depression and anxiety. Aaron says his mental illness means taking a laundry list of pills ... and he's not hiding anything.

Carter's reveal is just part of a 2-part interview on "The Doctors" this week. We're told along with focusing on his health, the segments will include Aaron's mom and her struggles with alcohol.

Aaron will also be taking a drug test to prove to the docs he's sober as he insists, but as you can see in the clip ... his admission to opioid use after a dental procedure already has eyebrows raised.

"The Doctors" interview comes on the heels of a tumultuous month for Carter -- despite him boldly telling us his mental stability has been "infinite" throughout.

It started in early August with him facing accusations of flipping rescue dogs for profit, then a few days later ... cops were called to his home over fears he was suicidal.

After a nasty, allegedly violent breakup with his girlfriend that resulted in a restraining order, Aaron was spotted buying guns ... and more guns.

All of this and more will be discussed on the 2-part interview airing Thursday and Friday. And, by the way, Aaron's 'Doctors' visit won't be his first ... his dependency on prescription drugs was also the topic 2 years ago.