The works of those who live according to God are the following: one man strikes his head all day long [I don't know what this is referring to], and does this instead of the hours of his services. Another joins together the set number of his prayers by preserving in continual prostrations. Another replaces the services by copious tears, and this suffices him, because it seems better to him than anything else. Another is zealous in the meditation of his understanding and limits his appointed rule to this. Another torments his soul with hunger to the extent that he cannot perform the services. Another makes his service unceasing by continuing in ardent study of the Psalms. Another passes his time in reading, and so kindles his heart. Another is taken captive as he comprehends the divine meaning of the divine Scripture. Another is restrained from his customary study and is held by silence in his astonishment at the wonders of the verses.
St. Isaac the Syrian, Homily 6
St. Isaac points out to us that it is normal for each person to find a warm heart and grace-giving prayer in different activities. People often confide in me that they find their prayer rule to be little more than an exercise they force themselves to do. There is no life in it for them. When people tell me this, assuming that they have persisted in the rule for a while, I suggest that they find a different rule. One's prayer rule should be life-giving, not life-draining.
Certainly, we must all force ourselves to pray to a certain extent--especially at the beginning. But if prayers do not blossom forth into prayer, into communion with God; then probably it is time to change your prayer rule.