Jessica Simpson -- Look At How Much Weight I've Lost in 4 Months!

Jessica Simpson proved getting back to her pre-baby weight is a losing battle ... by showing off her slimmer figure after another workout in L.A. on Tuesday.

Jess has griped about how tough it's been to shed the poundage ... claiming her boobs are so tremendously huge, she can't go jogging.

Still, it's obvious the 32-year-old mom has made some progress in the four months since she gave birth to daughter Maxwell.