Tattling Sources say doctors at Promises Rehab Facility, where Britney Spears is currently “enjoying” a luxurious stay, think the underlying reason for her trouble may be post-partum depression.

Britney’s doctors have two operating theories — either that she suffers from post-partum depression or bipolar disorder. The doctors strongly believe post-partum is the problem.

As for substance abuse, as one source says, “No doubt about it – she likes to drink.” But doctors believe the drinking is a way Spears has coped with a bigger problem.”