I often great head ache around my right eye n behind the eye. I often suffer from constipation. Is it because of this.?

Headache constipatio. No headache does not cause headaches.
Probably not. Not sure if you're asking if constipation is causing pain in the eye, or if the pain in the eye causing the constipation. Either way, they're probably not related. Pain in eye can be from cluster headaches, referred pain from sinus (i suppose straining from constipation can worsen sinus pain which can in return feel like an eye pain) and dry eyes, and rarely severe glaucoma.
Occipital Neuralgia. Headaches behind the head and that travel up to behind the eye are frequently occipital neuralgia. These headaches are caused by pinching of occipital nerves which pierce through the scalp muscles at back of the head. Treatment is directed at relieving the spasm of these muscles. Occipital nerve injection is almost 100% successful at symptom relief. Pain medicine may be causing constipation.