I am bulimic, lately it has been harder and harder for me to vomit. Why is that?

Psyche vs Mechanics. Purging (purposefully vomiting one's food) is a hallmark symptom of bulemia nervosa. Finding it increasingly difficult to vomit is likely due a physical or psychological cause. Vomiting can cause esophageal tears or spasms which would make it more difficult to vomit. The stigma associated with vomiting may make it difficult to vomit as the mind can be powerful. Seek medical attention right away.