Dark gums is likely just normal pigment. You are welcome to send a photo for me to assess.
I'm glad he doesn't seem obviously unwell and has managed to drink and eat a little, which is very reassuring. Hopefully he keeps this down.
Certainly, if he feels nauseous, it would be expected for him to eat less and to be acting subdued.
Given he has no other signs, I would advise to monitor at home for now.
For the next 24 hours, I'd feed a bland diet of e.g. cooked chicken and rice, to help his stomach settle. I'd try him again in the morning. Do allow water drinking at all times.
To help with his stool, you could start a probiotic anti diarrhoea paste such as Protexin Prokolin which you can get online or from a pet shop.
When it comes to a stomach upset in young dogs, we usually find they improve rapidly.