Why am i not losing anymore weight?

ive been working out about 4 months now and have lost about 70 lbs i started at 393 and im now down to 321. When i started i was doing about 3 miles a day on the treadmill or elliptical and about 45 min in the weight room but now im up too 4.0 to 4.5 miles a day and 30-45 min in the weight room just depending on how i feel. and im stuck at this weight and i want to get down around 230lbs can i get some help....i work 12 hour swing so its hard to stick to a diet cause my eating schedule changes every 2 weeks but i do eat very healthy lots of fruit veggies tuna and whole grains soy milk that kinda stuff. like today i had Breakfast: egg sandwich on whole wheat bread snack: banana nectorine lunch: thin whole wheat bagel laughing cow cheese wedge and a starkist tuna creations and some grapes afternoon snack was grapes and for dinner was the same thing i had for lunch and i drink about a gallon of water a day ....im just looking for some pointers so i dont get discouraged thanks!