When did you start working out? You do not get your mass over night, it is a long process which needs time. It is very common that we do not directly see the mass differenceses because we see ourself everyday in the mirror, do you understand?
And i can only give you the same advice like pur3lydriv3n (damn, what a name:-D), you have to add more to your daily intake, but when you already did this, the the answer is: time. the results will come, but slowly and they require hard work.