Wife of 'Biggest Loser' Doctor Robert Huizenga: He Got a New Young Thing ... I Got a Tumor

Ex-'Biggest Loser' doctor Robert Huizenga has a big problem with his ex-wife ... who says she's cash strapped and fighting illness, while he's off living the life with his 34-year-old P.Y.T.

Wanda Huizenga says she and the Dr. were happily married for 33 years -- plus 3 not-so-happy years -- and during that time she quit working and became a full-time mother and housewife. They split up in 2012, but since then ... Wanda says she's fallen on hard times. She's battling COPD and has a brain tumor.

On the other hand ... Wanda says Robert, who is currently Charlie Sheen's physician, is having the time of his life. In legal docs she describes his health as, "Excellent. Runs 8 miles a day. Young 34-year-old to keep him happy."

Dr. H. is currently paying her $10k per month, but Wanda says that's not cutting it ... especially with her medical bills. She says her ex is not "being fair or generous" and she's hurt beyond belief.