Hi i have a serious yeast infection and i used monistat 1 (tioconazole) day cure and itch lastnight but it still burns and itches really bad what should i do?

It takes a few days: Monistat usually is effective against vaginal yeast infection, but it takes a few days. Are you certain of the diagnosis? For such serious symptoms, you should not be treating yourself without professional advice. Additional treatment may be helpful (e.g. steroid cream); and also to make sure it's not something else. For example, initial genital herpes can mimic severe yeast symptoms.

Use Monistat 7 for the complete 7 days. If that doesn't work lease bring this up with your Gynecologist who knows your medical history. If you don't have confidence in your Doctor see another for a second opinion.