Nick Young's Ex: I'M 22 WEEKS PREGGO ... I Don't Feel Guilty

Nick Young's baby mama just revealed she's 22 WEEKS PREGNANT with his second child ... but says they were messing around behind Iggy Azalea's back for A LOT longer than that.

The woman, Keonna Green, just broke her silence to US Weekly -- dishing all the dirt about her secret affair with the NBA star while he was still engaged to Iggy.

Keonna -- who already has a 4-year-old son with Nick -- says they reconnected romantically BACK IN SEPTEMBER.

Keonna says she advised Nick to come clean to Iggy -- "I would be like, 'Nick, you cannot be sloppy. You need to be honest [with Azalea].' He would say, 'I don’t want to hear it.'"

She also says she doesn't feel guilty -- because "I’m pretty sure I’m not the only woman."

As for her message to Iggy -- "I wish her a lifetime of success … I mean, I’m definitely not going to apologize for being in love with a man who I have a lot of history with. I do wish her that kind of success and hope that she can get through this difficult time and she and Nick can move forward from this."