Hello, I would be happy to help you with your questions.
Based on the negative urine and blood pregnancy
tests, you are not pregnant.
The explanations for irregular bleeding include:
1. Irregularity in terms of when you ovulate - this can lead to skipped periods and irregular bleeding
2. Anatomical changes such as polyps or fibroids
You need an exam and an ultrasound!
I hope that this helps and good luck!