Hi Suzanne -
Food sensitivities can show up in a variety of ways, including bloating, abdominal pain, gas, skin rash, itching, etc. But if weight maintenance is the only symptom I would not think it is a food sensitivity but I do not know your health history. I would recommend that you discuss this with your doctor. I often suggest that people try an elimination diet or food rotation diet as described in the article below if they suspect that they have a food allergy or sensitivity. I have included the link here.
http://www.vitaminshoppe.com/content/en/healthguide/hncontent.jsp?org=VSI&ContentID=1292009&category=Diet&title=Low%2DAllergen%20Diet&type=
Regarding snacks, if you are hungry at 9 PM I would eat a snack with protein to keep you alert and focused for your evening. Here are a few snack ideas: a fruit or vegetable with 1-2 tablespoons of peanut butter, 1/4 cup of nuts/seeds with a fruit or vegetable or 1/2 sandwich on 100% whole grain bread with 3 ounces of lean protein, like turkey, dark green lettuce and other veggies and 1/2 oz of cheese. Your snacks should have protein with a some fat and either a fruit or vegetable or both. Also make sure you are drinking plenty of water. Slight dehydration can you make tired and sometimes make you feel hungry. If you urine is light yellow or clear, then you are drinking enough fluids.
You may want to consider taking a multivitamin/mineral supplement, a calcium/vitamin D supplement and a fish oil supplement. Consider a fish oil supplement if you eat fish less than three times a week.
Finally if you have maintained the same exercise rountine for more than a month, I would recommend you change it by increasing your workout's intensity or duration to help you body burn calories.
I hope this information is helpful!
Christiane Rivard, MPH, RD