Plateau Help

I have lost about 40 pounds since January 2013 but the end of last year I stopped losing weight. I have adjusted my calories several times and my exercise routine. I do understand that your body gets use to things really easily. But I really need help at this point because I have not a clue about what I should do now to start losing again. I eat 1500 calories a day and exercise 4 days a week. I eat most of my calories before 1pm and a small amount of calories for dinner. Please help!