Blac Chyna -- Tyga's Been After My Ass for Months

Blac Chyna says Tyga didn't just text her out of the blue this week trying to get back with her ... she says he's been making that play for 7 months.

Sources connected with Blac Chyna tell TMZ ... the text -- in which he said "I want to be with u" -- was the last in a flurry of texts, conversations and private face-to-face meetings in which he made his play to reconcile their relationship.

Sources close to Chyna says she never believed he was physically with Kylie Jenner -- partly because she's 17, and partly because they were all neighbors and close to the Kardashian family. She says she believed Tyga when he called out the media for suggesting he was dating Kylie, but doesn't believe it anymore.

Blac Chyna posted Tyga's texts out of anger, but she claims she wants nothing to do with him anymore. It's complicated by the fact that they have a kid together.

As for Tyga, he has never said he's with Kylie and in the past has denied it ... but he's recently insinuated it, and even put it in writing.