Why is my weight loss at a stand still?

I started my weight loss journey late last year.. and lost almost 30 pounds in 2 months. I was 407 pounds in late February, and i when i weighed today for the first time in a month, guess what my weight was? 407. It was so discouraging and disappointing. It made me feel like all of the hard work I've been doing is for nothing. I can't understand what went wrong.. i always stay under my calories.. actually under what is recommended for me. The only thing i can think of, for the first two months when i lost that weight, i was on a low carb diet. Under 50 carbs a day and that worked for me. But last month i got sick of all the restrictions i had so i switched to a basic low calorie diet. The only foods I've added are bread and occasionally some whole wheat pasta. Could it be that my body only responds to the low carb diet? What could i do differently?