Two or three games is very little to say much. You will not even have encountered all of the main lines after ....a6. Generally the Najdorf Sicilian is rather tactical and opening mistakes can quickly lead to a loss. In some lines white has a very straightforward plan of pushing its h and g pawns and checkmating black.
Practising tactics and studying the opening thoroughly is essential. For more useful advice it would help to know your playing strength and to see one of your games