An adult dose of Zathrin (Azithromycin) for throat infection/pharyngitis is 500 mg once per day for 3 days.
You have consumed 300mg per day which in within safe limits. So please don't panic.
The vomiting might be a side-effect of Azithromycin.
Next Steps
Wait for 36-48 hrs from the last dose of Azithromycin. Vomiting will subside spontaneously once the drug is cleared off from the body.
Health Tips
If vomiting persists, meet your doctor.