Can stress, overfatigue or anxiety trigger back pain?

Yes. Among many other physical symptoms. It's a great reason to resolve those issues in CBT therapy or w/ mindfullness meditation, yoga, etc. Do it! So many hings will feel better!
Yes, possible. Yes, chronic or severe stress, overfatigue, and moderate to severe anxiety can cause a variety of physical symptoms, including back pain. But you have underlying medical conditions: multiple fibroids, surgery and biopsy? Your back pain may be due to a medical condition, check with your dr. If he/she says not physical, consider some CBT psychotherapy for stress and anxiety with a psychologist.