You should be getting more eggs than that, but there are many reasons that this could be happening. First of all, do your hens roam around unsupervised during the day? If so, they could be laying eggs in places other than the nest box. An egg search might be a useful thing to do.
Next, I would check your flock for mites/lice, as infestations of those can cause, among other things, a drop in egg laying. Look on the feathers and skin near the vent, under the wings, and beneath the hackle (neck feathers). Mites will appear as moving black specks, while lice will show up as larger yellow blobs and eggs stuck to the feather bases. Treat by dusting with 5% Sevin dust, poultry dust, or by spraying with another mite/lice spray. Clean out the coop, spray it down with vinegar or liquid Sevin, and then put in all fresh bedding.
Also, has anything stressful (predator attacks, excessive heat, noise/construction nearby, etc.) been happening in your area? Stress can cause a decrease in egg laying as well. In the case of predators, securing the coop should be effective, and your hens will return to normal once they settle down. To combat heat, mist your birds with water, give them frozen fruit, and put ice cubes in their water to help them with that. If noise and other disturbances are a factor, once that stops, your hens should go back to normal. A bullying hen could be causing stress too, so I would observe your flock and think about isolating problem hens if necessary.
In addition to the above things, I would check your hens for any signs of disease--swelling, nasal discharge, abnormal respiratory sounds, weight loss, blood in the droppings, etc. Treat them, if necessary, as disease is another stress-producer.
Shorter day length could be the problem, too, as chickens usually stop laying (or at least egg production decreases) once daylight is less than 14 hours.
