Dear meghanmp: It can be very difficult to accurately diagnose a miscarriage unless there has been at least one positive pregnancy test. Given your mom's history your best bet is to see your GYN or clinic. They can do a blood pregnancy test which are accurate down to only 5 units of HCG pregnancy hormone (urine tests are 20-50 units).
The pain and fatigue/nausea could also be from an ovarian cyst, an infection inside the uterus, or even a bowel condition (eg diverticulitis). You need a focused abdominal/pelvic exam and possibly an ultrasound if the pain seems to be from the ovary.
Yours,
Jane