Besides the lemon flavor what is the difference between thick & easy and thick-it in nectar consistency?

I can't say, as we've only gotten thick-it in powder form. Buying the pre-thickened water saves a lot of time and effort

What is the calories in it and the carbs?

It sez 5 calories per serving. Each bottle is 4 servings

It does not say on the Product Information if this can be heated. Please see additional information about the product: Manufacturer # 12863 Brand Thick & Easy® Hydrolyte® Manufacturer Hormel Food Sales Application Thickened Water Calories Per Serving 5 Calories Consistency Nectar Consistency Container Type Bottle Flavor Lemon Flavor Ingredients Water, High Fructose Corn Syrup, Modified Food Starch, Contains 2% or Less of Citric Acid, Salt, Sodium Citrate, Natural and Artificial Flavors, Potassium Citrate, Tricalcium Phosphate, Glycerol Ester of Wood Rosin, Potassium Sorbate and TBHQ (Preservatives), Brominated Soybean Oil, Ascorbic Acid (Vitamin C) Preparation Ready to Use Product Dating McKesson Acceptable Dating: we will ship >= 90 days Serving Size 8 oz. Serving UNSPSC Code 42231806 Volume 46 oz. Features Thick and Easy Thickened Water Hydrolyte nectar consistency or IDDSI level 2 Refreshing thickened water with a hint of lemon for those with dysphagia Thickened with clear thickener for natural water appearance