Work out: No muscle mass?

I'm pretty thin, and don't have much body fat

When I work out, I just DON'T gain muscle mass, I get toned. I do 40 wide push ups, 20 triangle push ups, 40 sit ups, and leg lifts.

So my question is, what should I do to gain more muscle mass? Stick to the routine? Get a new routine? I won't drink Whey protein because I don't want to gain all sorts of weight when I get lazy!

Any help, information, or knowledge is greatly appreciated

Thank you
Updates
+1 y
I do intend on replying to all of your answers, for they are all very helpful!


So I haven't forgot, and thank you for the wisdom guys!
Work out: No muscle mass?
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