britney.jpgBritney Spears’ baby joy has turned into baby blues! "Britney is down in the dumps and cries at the drop of a hat," says a friend of the 23-year-old pop tart, who gave birth to Sean Preston Federline, her first child, on Sept. 14.

And, says a source, she’s sleeping late, sometimes until 2 p.m., and avoiding visitors. Adds the Spears insider: "She must feel totally overwhelmed. All of a sudden, she has this baby who relies on her for every single need."

Britney is upset she can’t even begin taking off some of her pregnancy weight because she had a C-section just three weeks ago. The 5’5" singer, once a svelte 105 lbs., gained 50 lbs. during her pregnancy (the average gain, according to doctors, should be 25 to 35 lbs) and must wait three more weeks before she can begin to exercise. "Before she got pregnant, Britney could drink venti Starbucks Frappuccinos, eat McDonald’s and still stay thin," says a friend.

"Now the weight just hangs on her belly. She must feel like she has the figure of a middle-aged woman, but doctors insist she not try vigorous exercise until the baby is 6 weeks old."