I think i might have gotten a scab in my mouth from a drink. can something happen for having someone else's scab in my mouth?

Contagious? yes: The virus that causes cold sores is herpes simplex 1, or HSV-1, a cousin to the herpes simplex virus 2 that causes most genital herpes. More than half of all Americans are infected by type 1 herpes by the time they're in their twenties, so "common" might be another apt description for cold sores. they're actually contagious from the time you first feel cold sore symptoms, till they heal.

Relax, Canker sores: Most mouth ulcers, canker sores, will clear up by themselves within a week or two. You should see your GP or dentist if the ulcer gets worse or lasts for longer than 2 weeks. Take care.