What could be the problem if im having pain in my left ovary with back pain and a cycle that changed from 29 days to 35 days and not being able to fall pregnant for 2years?

You could be having ovarian cysts which would cause no ovulation for that cycle and extend the length. Talk to you gynecologist about having an ultrasound when you feel the pain. they can check for cysts and recommend prescription medication or hormones to regulate your cycles.

There are many reasons for such complaints, but you need to be evaluated by your primary care provider or your gynecologist.