Diddy‘s sobriety journey took a detour in lockup this week … TMZ has learned he was drinking behind bars and got in some trouble with prison officials.

Sources with knowledge tell TMZ … Diddy had some homemade alcohol in Fort Dix, the low-security prison where he’s doing time. We’re told the alcohol is made of Fanta, sugar and apples, which inmates give two weeks to ferment into an alcoholic substance.

We’re told Diddy got caught by jail officials and prison officials planned to move him from his old unit into a new one. Two sources tell TMZ prison officials have now reversed their decision and Diddy will stay put.

You may recall Diddy made a big deal about his sobriety to the judge prior to his sentencing last month … telling the court he was sober for the first time in 25 years. He also said he lost his way due to substances.

He wrote in a letter to the Judge, “The old me died in jail and a new version of me was reborn. Prison will change you or kill you — I choose to live.”

We shared pictures of Diddy hanging around the New Jersey prison yard last week, and he seemed to be the life of the proverbial party — laughing and smiling while shooting the you-know-what with his fellow inmates.

Diddy was convicted on two counts of violating the Mann Act back in July and received a 50-month sentence in October. He was transferred to Fort Dix last week.