Final answer:
The patient's most likely diagnosis is uterine fibroids based on the symptoms and physical examination findings.
Step-by-step explanation:
The patient's most likely diagnosis based on the provided information is uterine fibroids. Uterine fibroids are benign masses of cells that can cause heavier and longer menstrual periods. The irregularly shaped 16-week size uterus observed during the pelvic examination is consistent with the presence of fibroids. The patient's hematocrit of 28% supports the possibility of excessive menstrual bleeding.