How many times you gave up on your purposes only because somebody had a got at you? Answer yourself question: Are you living for to make others happy or to be happy and share this happines with others?
Don't forget about your purposes, your dreams, your desires. Strive to achive them. Listen those people which want you to be happy, those which in worst case give you helpfull hand...not those which are telling to you what you're doing is wrong and have no sens, etc, etc.
Remember - that kind of people, pessimist, always will be around us and they always will be unhappy. If you'll meet some of them, count till two: one, two…one is you - your happines - your live - your feelings - your thoughts...and second, second is the rest of the World. You're the most important person in the World.
Do you know definition of insanity?
"[…] doing the same thing over and over again and expecting different results." (A. Einstein) If you're doing something without results you expect…change the way that you're doing it.
Don't think about past, don't think what will future be. Focus on present and do all the best you can. "Start where you are. Use what you have. Do what you can." (A. Ashe)
"Whether you think you can, or you think you can't - you're right." (H. Ford)