What else can I try to get my 12 month old to sleep through the night?

My just turned one year old still wont sleep through the night! Around six months he was down to waking only once a night, and then we had some unexpected company for about a week. With them long gone, you'd think that he would be able to sleep solidly. He only has about two naps a day, and is very active (he started crawling at less than six months, and walking at nine). I know that part of the problem might be that I don't have a set schedule at work. I work two late evenings and three mid-day shifts. But his sleep pattern has not varried. His nap times are about the same every day, and when he wakes at night (three times on average) it's always around the same times. I just don't get it. Is there something wrong that I may not know about? Am I missing something here? I need help, and sleep, and soon!!