You can google "calorie calculator" and several will come up, or you can do it the easy way and start MedHelp's Food Diary. Once you put your stats into the diary, it will calculate your daily needs. If you prefer to tell me your age, current weight (still 150?) and activity level (apparently low?), I'll be glad to help you.
How do I calculate how many calories I need each day?
It would appear that you aren't eating enough calories and may be eating the wrong types of foods.
Your body needs a certain amount of calories in order to function properly. If you don't provide enough food, your body will hold onto existing fat stores because there's not enough calories coming in. This is called "starvation mode". You should calculate your calorie needs, based on current height, weight, age and activity level.
While fruit is good for you (apples, pears especially), most fruit has high sugar content and should be limited to 1-2 servings/day. Bananas have high sugar content and if not used (with exercise), will turn to fat. Most veggies are considered "free" if they are eaten raw or steamed with no added fat, so they're your best choice.
While turkey is good for you (the less processed the better), the type of bread being used in the sandwiches is very important. If you aren't using a whole grain bread, you are defeating your purpose. It also depends on what you are adding to the sandwich. Butter, mayo or other "fat filled" condiments will, again, defeat your purpose. Feel free to add plenty of lettuce, tomatoes, cucumbers, pepper strips, etc.
While 3 servings/day of dairy are usually recommended, make sure you are opting for the low/no fat varieties.
Eggs are an excellent "diet" food, because they are low calorie and full of vitamins/minerals, but if eating them fried, watch what you fry them in, because added oil or grease can really increase the calories.
Oatmeal is excellent, also, but what you put on it might change that quickly.
Exercise is key to weight loss, as it tones the muscles, conditions the heart and increases strength. If you don't use the calories you take in, they will end up as fat. Walking is always an excellent type of exercise - try for 30 minutes/day and work up if you can. Yoga is also excellent for toning and weight loss.
All of that said, I'd also recommend that you get some blood work done to test for thyroid function (get TSH, Free T3 and Free T4) and insulin resistance, as well as PCOS.