What is the reason for lower back pain after a painless abortion with a little blood?

Patient's question:

Married
December 3rd, I had an abortion under anesthesia. After the surgery, I didn't bleed at home. By the end of the year, there was too much work, so I went to the office on the 6th (the range wasn't large, mostly around the computer). On the 7th, there was a little bleeding, and it still is a bit today, like the days after each menstrual period. Another thing is that sometimes I have lower back pain, but I can't pinpoint where it hurts! Starting today, I'm resting at home. Is this serious? The Western medicine prescribed by the doctor is almost finished now. What should I do! Thank you
First follow-up question: There is a test report:
1. White

Doctor's answer:

Because the earlier an abortion procedure is performed, the simpler and safer it is. Conversely, if the procedure is delayed, it becomes more complex, and the recovery time after the abortion also extends. Since the uterus is not yet significantly enlarged within the first 10 weeks of pregnancy, and the fetus and placenta have not yet formed, it is generally unnecessary to dilate the cervix, making it easier to remove the fetal tissue. Postoperatively, attention should be paid to local hygiene, and sexual activity should not be resumed prematurely to avoid infection, especially genital tract infections such as endometritis or salpingitis. If fever or prolonged lochia occurs, it is important to seek medical treatment promptly.