Rachel Zegler Begs Fans on Instagram for Help With Sick Dog

Rachel Zegler's crowdsourcing help for her sick dog ... explaining that two different veterinarians she's been to have done nothing for him -- so, she's going to the amateur pet doctors on social media instead.

The actress took to her Instagram story Sunday morning ... telling her 2.5 million followers that her pup, Lenny, is in a bad state -- and, she's at her wits end trying to help him.

Zegler says she's been to the vet multiple times over the last few days ... but, her dog is still experiencing bad stomach issues and no appetite.

Her mom is making her dog a ton of chicken and rice, Zegler adds ... but, it's not enticing him to eat -- and, she's really worried about him 'cause she has to "fly across the ocean" in a couple days.

While he's clearly not feeling 100%, RZ says her dog is still playing and they can't feel any growths in his stomach -- so, she just doesn't know what's wrong with him.

Rachel also says if one more vet tells her to just take Lenny home and let him wait out his symptoms while he's "in so much discomfort and literally spraying all over my apartment with such urgency" then she's going to lose it.

Lenny just turned two last month, BTW ... and, Zegler shared a heartfelt photo collage to celebrate her little guy's bday -- writing life is better with him in it. She's clearly obsessed too, 'cause her Instagram bio reads "lenny's mom."