Problem: Pace bowling issues

[Eclipse1123]

On the first few deliveries of every over I bowl well and they can't hit me when I straighten the line up they hit me for four. The next over they seem out of their depth and miss most of them and stays in. The next over I go for over 10 runs and still no wicket. Can some one please tell me what I'm doing wrong.
I bowl a good or full length and am a left arm fast bowler.

 

[ravenswood7]

On the first few deliveries of every over I bowl well and they can't hit me when I straighten the line up they hit me for four. The next over they seem out of their depth and miss most of them and stays in. The next over I go for over 10 runs and still no wicket. Can some one please tell me what I'm doing wrong.
I bowl a good or full length and am a left arm fast bowler.

look for batsman's weakness if they are weak against short balls i.e back foot flat bat shots ball bouncers I know u cant bowl 6 in a row if there weakness is straight bat front foot ball fuller but mix your length up sometimes bowl slower balls faster ones I find this helps I know its hard sometimes being patient but batsmen will make mistakes after a while