Sources with direct knowledge tell TMZ ... Madonna's been vomiting uncontrollably since being discharged from the hospital, and the infection is still wreaking havoc on her body.

We're told Madonna is still too sick to even get out of her bed at her New York City apartment ... where she's been recovering since Wednesday night, when she was released from the hospital following a multiday stay in the ICU.

When Madonna was taken to the hospital Saturday with a serious bacterial infection, we're told she was metaphorically "kicking and screaming" ... protesting the decision to send her there.

Our source say Madonna's assistant was with her when she collapsed last Saturday, and that's when the uncontrollable vomiting began.

As we previously reported ... Madonna was dealing with a fever for more than a month leading up to her hospitalization, keeping it a secret from everyone. We're told she was afraid if she sought medical care, it might jeopardize the tour, which she's been working so hard to prepare for and posting behind the scenes shots of. The delay made the infection far worse.

Madonna's longtime manager Guy Oseary is already hinting her upcoming tour will be delayed -- her first concert was scheduled for July 15 -- but we're told no final decision has been made by her manager or agent.

For her part, our sources say Madonna wants the tour to go on as planned ... but everyone close to her is advising she press pause and allow her body to recover.