Bodybuilding.net - Bodybuilding Forum

I've been reading bodybuilding websites and bodybuilding forums for a while. I'm a natural sportsman. Played all kind of sports. Last year, I had my peak but if I knew what I know today, I could have achieved twice what I got.
After I graduated, life isn't the same and you kind of get loose. I'm now trying to gain weight, my diet is now more developed and I already feel the effects of two months of muscle building with whey etc.
Now, I feel I have reached the max. Everytime I "lift" I stay the same. Don't feel that growth anymore.
I'm 19, 1.72m and weight 57kgs. I train at home, as my objective isn't to be a world class lifter but get a good shape. I'm rather skiny as my body fat is very low, but the six pack cannot be seen (for example).
The help I would like from you guys is to gain a general boost. This is, I do pushups, with my legs raised, arms apart, arms close, everything. I pull myself in between chair, the one that works lats, triceps. For all of these, I do 3x15.
Do you think my body is getting used to the workout I do? I do vary everytime but there are a limited amount of exercised to do without weights.
What I feel is that I'm missing something on the equation. Is I did before, with the Whey. I think feel the problem is with what I do and how I do.
Thank you very much, firstly, for reading this essay, hihi; secondly for the help you may give me.

Don't think twice in helping and giving tips.
Thank you,
Fred