Bled mid-cycle for 6 days. Bleeding enough to leak/overflow through liners. I am now 12 days late for period but several negative hpt. Whats going on?

Hormonal imbalance. If you did the test correctly and it was negative at 12 days after a missed period, you are unlikely to be pregnant. Menstrual irregularities are not uncommon and anovulatory cycle is a common cause. If you miss more than two periods it would be time to see your doctor. If you do not wish to be pregnant, use contraception all the time. You may consider implanted contraceptive or an IUD. Consult this site for more information on this topic. Practice safe sex. Get HPV vaccine.