Justin Bieber and Sofia Richie are celebrating her birthday in Mexico.

Us Weekly reports the pair are staying at Las Ventanas al Paraíso, a luxury Rosewood resort.

The couple confirmed their romance two weeks ago but the union was met with drama, as the pop sensation's ex-girlfriend Selena Gomez became embroiled in a public spat with the star.

The 24-year-old singer publicly scolded Justin when he threatened to make his Instagram page private after fans lashed out over pictures of his new love, and they accused each other of cheating during their on/off romance.

True to his word, Justin disappeared from the photo sharing site and Selena is now said to be stressed and needing time off work to rest.

A source revealed: "Justin and Selena's relationship is notoriously rocky and it hasn't been easy to see him move on so publicly with Sofia.

"But Selena is used to seeing him with other women - it's the combination of being over-worked and under pressure.

"She's been touring for four months non-stop and won't rest until mid-December with her 'Revival' tour still to hit Europe and South America.

"There's real concern and the plan is to talk to her in the next few days to ask her to consider taking some time off."