Vaccinated but got flu. on oseltamivir, but nothing for bacterial superinfection. is resistance or thick mucus more likely for why it's not working?

Curious statement: You have not provided any info that supports the idea it's not working.Tamiflu is not an antibiotic. It suppresses reproduction of flu virus & influences intensity of illness. It works best when taken in the first 12 hours of symptoms. After 48 hours the virus is so well established it does little. It might be resistant or just too late to be much help.