I think you sound like a nice person. The next time you bring in a doughnut, you might just bring one for yourself. If anyone comments you could say you were saving your money for a special trip, and then the next time you bring in a doughnut bring in just one extra for that person. (This is a way of asserting your individualism and recognizing your co-workers as individuals).

People who figure out you are sensitive and bothered by a disapproving look will likely use that on you. Try to cultivate an attitude of "I know I am a good worker, a nice person, and undeserving of dirty looks." If you continue to get disapproving looks, you can ask in a mild (not anxious) tone "Did you need something, Mr. Frownie?" Only don't call him Frownie unless that is his real name!

Remember you have the right stuff. You are worthwhile. You have your place in the world. Courage!