Prince: Operating Theory ... One Doctor, No Aliases

Prince got Percocet from one doctor, who always prescribed the drug under the singer's real name ... sources connected with the investigation tell TMZ.

Our sources say ... so far there is no evidence anyone other than Dr. Michael Schulenberg prescribed drugs for Prince. What's more ... we're told the doctor never wrote prescriptions using a name other than Prince Rogers Nelson.

This is in sharp contrast to Michael Jackson's drug abuse ... we broke the story MJ had scripts written by multiple doctors, and for at least 19 aliases.

Our sources caution there could be other doctors who prescribed meds for Prince outside the Minnesota area ... but so far nothing's come up.

It's an interesting turn, because the DEA monitors over-prescribing of drugs, yet we're told nothing had been flagged. It's evidence that Prince may have developed a sudden, life-threatening spike in opiate use, and it happened too quickly for the feds to notice.