'Biting my truant Pen...'- where does this line occur? What is meant by truant Pen? Why did the poet bite his pen?

The line occurs in Loving in Truth by Philip Sidney. 'Truant pen' means a pen that runs away. Like a truant boy the pen seems to run away. By studying the works of others and borrowing their materials and fit phrases for depicting his woes the poet finds it difficult to carry out his purpose effectively. So the pen he holds does not seem to obey his heart's desire or pay heed to his feelings.

          The poet bites his pen to indicate the state of his mental restlessness. He grows angry with himself for his failure to express his poetic feeling. It is well suggestive of a lover's psychology, his utter helplessness caused by intense Passion of love.