This compilation of symptoms is not specifically classic for any one condition and I would suggest that you schedule an appointment with your OB/GYN. When we think of irregular periods, we usually think of reasons why women would not ovulate. One such condition is called polycystic ovarian syndrome which is probably the most common reason why women don't ovulate and thus have irregular periods. Another possible reason is if you are an avid runner or you exercise in some other way very vigorously. Aggressive exercise or weight loss
can cause one to not ovulate. The symptoms of pain in your pelvis along with low back pain make me think of endometriosis
. This is a condition where parts of the endometrial cavity make their way out into the abdomen and cause pain usually during the menstrual cycle. Fatigue and loss of appetite are also common with this. Both of these conditions can be evaluated and/or diagnosed by your OB/GYN. I would suggest that you schedule an appointment with your OB/GYN for further evaluation. The first step is for you to describe the times when you have had a period over the last few months so that they get a better understanding of how regular you are. You'll also need a pelvic exam which can be helpful sometimes in diagnosing endometriosis. A pelvic ultrasound
might be warranted as well. Good luck.