You are trying too hard, I know what you mean.
Start simply by focusing on the breath and your natural rhythm and then count the breath in and out, e,g, in 1,2,3,4 out 5,6,7,8
The brain's like a computer, in Yoga we call it the 'monkey mind' jumping from one thing to another. The very act of trying to 'clear' it is a process. You need to centre on one thing only. The breath or a mantra is the best start. Bit difficult to help at a distance!