Why do I literally smell like vomit?

I have been smelling something on myself for a few days that smells like vomit. I brush my teeth regularly and thought that the smell may be coming from my underwear because since I’ve been on nexplanon I’ve had irregular bleeding. I do not think it’s down there and I’m starting to think it could be my mouth, but my hygiene is fine. It seems like I have a blister or something at the top of my gums as if my lining is too thin and the teeth underneath are almost being seen. Help????