Buddhists how to easily eradicate selfish desires?

I have given a lot of charity with the intention of receiving karmic rewards.Now the case is that I am not enjoying anything in life.Everything seems boring and lame,and I have lost the true Generosity I possessed..I was so happy before and was generous to my friends and others.Now I feel that selfish desires have caused me this.How can I remove them,and retrieve the "True Generosity" I possessed.