You need a proper balance of food and exercise, along with an adequate amount of sleep.
Did your personal trainer (or anyone else) help you figure out how many calories you need each day? You can't just pick a number (like 1000, 1200, etc) and drop to that amount of calories. Your body needs a certain amount, just to support the function of your organs, and if you don't take in enough calories, your body will hold onto current fat stores in order to stay alive.
I agree with sunnieday regarding eating only when you are hungry, but eat EVERY time you get hungry. Keep your portions reasonable. Instead of sugar, opt for Stevia or agave nectar for sweeteners, rather than artificial sweeteners.
Also, remember that "low/no fat" is not always the best option. Fat actually adds flavor to foods, so many times when manufacturers remove fat, they add extra sugar to make up for the lost flavor. Same goes for "sugar free" - fat is often added to enhance the flavor.
Your body needs a certain amount of carbs, but stick with the complex carbs that take longer to break down, such as whole grains, veggies, beans, etc. Eat lean protein, and don't forget the "good" fats, monounsaturated fats (MUFAs). I don't necessarily recommend that you go to full fat dairy, because of the unsaturated fats; however, that would depend mostly on your overall health and should be determined by your doctor.
I'd also wonder if your thyroid is functioning properly. Your thyroid largely controls your metabolism and if it's not functioning properly, you won't be able to lose weight.
I meant to add that once a week or so I feel like a fizzy drink. When this happens I choose pepsi made with real sugar. ( as opposed to artificial sweeteners) just once a week or so like I said. This satisfies my craving. Soda is horrible for you, but I find if I try to avoid a craving I just end up eating a whole bunch of other crap and I would have been better off just having the one soda. All in moderation. If you aren't clear about anything I said just ask and I will try to answer better. Good luck woman!!
Many will disagree with me I am sure but I am of the school of it's 90% what you eat and 10% what you do. I think you are possibly doing something not quite right with the food choices? I posted a thread about my very strange weight loss I have experienced over that last 2.5 months .... You can look for it but I will tell you here briefly in case it will help you. Throughout my adult life I have weighed around 120 to 125 lbs. I am 5'4, 35 years old. Two years ago I started drinking diet coke. I just enjoyed it so much and I thought I was making a better choice as far as soda goes with all the sugar. Well I didn't put it together at the time but I started craving the most terrible sweets and basically junk food which I had never done before. I proceeded to gain weight and went up to 144 at my highest. For me that was quite chubby. I thought it was just from passing thirty and getting older. Well one day I woke up and just like that I didn't want to drink the diet coke anymore. My body just didn't want it. So I stopped and guess what?? I lost 30 lbs in two and a half months doing nothing different except for this: I found nestea makes a 50% less sugar iced tea mix. It has no aspartame and believe it has no caffeine. I made up 2 one litter pitchers of that every night but I used much much less than the directions state. I just get bored of drinking water and this helps a lot. I drink the entire two liters everyday and sometimes three. I just use a couple of tbsp of the nestea mix per jug full. As soon as I get up I pour a glass and use a straw to help to drink it faster. As soon as the diet coke was gone ALL of my cravings left. I weigh 115 now. I just can't believe it. So I wonder if you might be using artificial sweetners in anything? Over to the food.... I can never do fad diets and I have never been able to follow any kind of low carb etc program. All it boils down to is biting a lot more calories than you take in. I eat full fat dairy because the other yogurts etc taste yucky and thin to me, and left me feeling hungry. I find having a regular cup of yogurt to be much tastier and actually satisfying .... But I have a proper portion. I do this with all of my foods. I don't ever deprive myself but I also never over eat. I only eat when I am hungry too. Eating this way has kept my weight low. My mom and sister are the exact same build as me but weigh a good 30+ lbs more than me. They are always going on some kind of diet, eating every four hours etc and can never lose any weight. They would never eat full fat dairy or the higher calorie foods but they stay at 140+ lbs. I have always been able to maintain a low body weight doing just what I told you now.... Except for my diet coke phase. I hope some of this helps! Are you following a 1200 cal per day diet?