STAYING clean and sober may be the best thing for LINDSAY LOHAN’s health, but it’s wreaking havoc on her waistline!

The “Mean Girls” star, 26,  has been eating more and has put on 10 pounds since clean­ing up her life earlier this year, going from her normal 114 to 124 in just a few short months, sources tell The ENQUIRER.

“Lindsay is happy to have her life back, but she’s bummed that her weight has shot up,” said a source.

“She’s complaining that all the weight she gains goes directly to her face and her legs, giving her thunder thighs.

“Lindsay is sick of people specu­lating that she’s had plastic surgery on her face. She’s puffy as a result of extra fat!”

LiLo’s new fuller frame was on display during a mid-August family beach-outing in Malibu.

“Lindsay usually loves to flaunt her figure, but she was careful to keep her shorts on to hide her upper legs,” the source divulged. “She was unusually modest, but it’s because she feels insecure right now about her body.”

Ironically, says the source, one of the main reasons the actress began abus­ing prescription drugs years ago was to control her weight.

“But with her career on the line, Lindsay is determined to stay the course , ” the source continued. “She’s thinking about signing up for Weight Watch­ers to help get her eating hab­its back on track. And even though she hates exercise, Lindsay realizes she needs to hire a trainer – or at the very least, get a gym membership.”

Lindsay, who has been through rehab multiple times, has been hard at work trying to turn her life around. She recently completed shooting the TV movie “Liz & Dick,” in which she co-stars as iconic screen legend Elizabeth Taylor.

Now, her friends are “play­ing dumb” about her weight gain because they don’t want to trigger a relapse, adds the source.

“They believe a bigger Lindsay is a much better alternative to one who’s wasted all the time.”