Hey Smooth,
It looks as if you have answered the question yourself.
"might be due to the fact that i've been doing the same weight all the time.(30kg benching and 15 kg bicep curls)"
I will take the bench press as an example. when you first started to bench at 30kg your body would not be used to it and the muscles would break down and repair, therefore growing bigger and getting stronger. However, if you continually bench 30kg week in week out your body gets used to the load and then will not improve. In fact there is more chance of actually getting weaker than stronger by using the same weight without adding more.
There is one program i can suggest for you. It is the Stronglifts 5x5 program. Look at the link below and download the free e-book. This program works really well for building strength and muscle.
http://stronglifts.com/stronglifts-5x5-beginner-strength-training-program/This program uses the main lifts, including Bench press, Squats, Military Press, and Pull-ups/Chin-ups. I went through a phase of doing 5x5 lifts and i will tell you now, it does really work the body. I have no idea on my 1RM on bench but i do know i can do 55kg for 5 reps on 5 sets, the last set is always a killer and when you get there you will see why it is so effective.
If you have been eating right then leave the protein shakes for now and focus on getting the weights right.
One last point, if bench and bicep curls are all you do then please do more. Do not forget about the muscles that you dont see in the mirror - Like your back, your calfs, your triceps. You need to work your whole body. There is nothing worse than seeing a guy with a built torso and twig legs, its just embarressing! lol.
Hope i helped,
Sean
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