Lindsay Lohan Hospitalized in L.A.

10/25/2004 at 02:55 PM EDT

Lindsay Lohan was admitted to a Los Angeles area hospital, her publicist Leslie Sloane confirms to PEOPLE.

The 18-year-old teen star, who was sick most of last week, entered the hospital last Thursday for observation. She was running a temperature of 103.

Lohan had been scheduled to tape a guest spot on boyfriend Wilmer Valderrama's sitcom, That '70s Show, on Thursday and Friday, but was forced to cancel, according to Sloane.

The last few weeks have been busy for the actress, who has spent days filming the movie Herbie: Fully Loaded and nights recording her first album.

Lohan didn't look well on Monday. By Tuesday, production had to be halted when she was too sick to work. "She was wiped out when she went into the hospital," says Sloane. "She’s going to stay till they figure out what she has and she starts to feel better."