'Teen Mom' Stars Catelynn Lowell & Tyler Baltierra -- We Need Couples Therapy

"Teen Mom" stars Catelynn Lowell and fiancé Tyler Baltierra might not be getting married as soon as you think ... TMZ has learned the duo has joined the new season of "Couples Therapy."

Catelynn and Tyler -- who infamously put their "Teen Mom" kid up for adoption back in 2008 -- have been on and off for over seven years -- but were reportedly set to tie the knot in Michigan in a few months.

Now, sources tell us, Catelynn and Tyler will hash out their problems on the Vh1 show ... about couples whose relationships are floundering.

We're told rapper Chingy, Flavor Flav and Joe Francis have also joined the cast ... with their current significant others.