I agree, check camera aim height. Remember a deer is only about 3 feet tall. Does your camera have any aiming indicator/check? Many have a "test mode" or some such where a red light shows when it would have triggered. Use this and when you walk infront of it, make sure you bend over to get lower.
I set my camera's about 2 feet off the ground, then walk infront of them and see if it looks right, where "right" means it looks like it is NOT looking me dead in the face, but lower.