Is it enough to pray when you feel like praying?
No. Someone who prays only when he feels like it does not take God seriously and will leave off praying. Prayer thrives on faithfulness. 
Posts tagged Catholicism
One cannot desire freedom from the cross when one is especially chosen for the cross. […] The more lofty the degree of loving union to which God destines the soul, so much more profound and persistent must be its purification.
Saint Theresa Benedicta of the Cross (Edith Stein)