I have this nagging pain behind my left eye I had it before but did not pay it any mind now it seems to keep coming back

Referred pain. The most common cause of your symptom is referred pain from occipital neuralgia. Ice and massage of the neck at the base of the skull can alleviate symptoms about 90% of the time. Occasionally the cause is inflammatory. See you specialist eye md to be sure.
Pain. Pain behind the eyes is a very common complaint seen in the general ophthalmology practice. The cause of this can vary tremendously, but fortunately are often times benign. Many of the causes of pain behind the eye can be traced back to sinus problems. However there are many other causes of eye pain that need to be ruled out by an ophthalmologist. It would be best for you to consult with your local ophthalmologist for a full evaluation.