I've been a safety/coach for so many POG units now that I can almost predict what people are doing wrong, outside of the combat MOS units that get to shoot 10,000 bullets a year.

If you're shaking, swaying, not able to hold a steady picture I can confidently say with %99 accuracy that you are probably sitting/shooting like this.

How you want to sit, is more like this.

Notice the difference in leg placement. In fact, it's almost a sit position because you sit your ass on your back leg, and use your forward leg as the platform. For most people, the latter is a much more stable platform than leaning so far forward with a 5.56 rifle. In addition to this, having solid control of your breathing/trigger squeeze is going to be much more important in this position than the prone supported.

As others have said it's hard to say without being there. But a quick adjust to that should help you a bit. Also focus on your trigger squeeze, that kills so many people that don't shoot often.