I have pcos and just got my period for the first time in months. I have really bad lower back pain and my breast are sore. Is this normal?

Yes. When you get a period after so many months specially with PCOS, your periods may be heavier and more painful. Your breast can also be sore. Please see your doctor to see if you need an endometrial biopsy. Patients who have long term PCOs need to be monitored for endometrial hyperplasia a condition that results for unopposed estrogen in PCOS. Good Luck!
PCOS. Polycystic ovarian syndrome (PCOS) usually prevents ovulation, and hence prevents periods. Spontaneous ovulation can occur, however, and the symptoms, since it is so seldom, can be just as you describe. Consult your healthcare professional, who may suggest oral BCP, which can prevent some long term effects from PCOS and "unopposed estrogen" which accompanies this syndrome.
I guess. Some women do have And and Back pain from Menstrual cramps and also get Breast Engorgement during Menstrual period. So this is normal. As you do not have regular period yo may be experiencing more.You may want to consider BCP, other specific medication to regularize the period and Premenstrual Symptoms.