John Proctor, though an apparently confident and calm man on the outside, is definitely struggling with some issues on the inside. The first issue that he struggles with, and the main one he battles throughout the course of the play, is a feeling of being unworthy and a sinner. He feels like he is a false man, a hypocrite, walking around like a good person when on the inside he knows that he has committed an awful sin. This hypocrisy bothers him, his sin bothers him, and he is conflicted about it. It bothered him so much to be having an affair and hiding it from his wife that when she suspected him of it, he "wilted, and, like a Christian...confessed" his sin to her. He then ended the affair with Abby, and has been striving ever since to make up for it. He tells his wife that he has "not gone from here to there without thinking to please" her, and is desperate to make up his wrongs. His sin with Abby has made him unsure of himself in his own eyes, in the eyes of his wife, and in the eyes of god. He feels a sinner, and not worthy of the veneration that many others that he knows has.
It is his feelings of inadequacy and sinful state that almost make him confess to a lie at the end of the play; it isn't until he feels he has paid for his sins and come clean with god that he feels okay with himself.
Another issue that he struggles with is a strong distaste for the minister of the town, Reverend Parris. He can't stand Parris's style of preaching "only hellfire and damnation," and finds Parris's fixation with money to be repugnant. As a result, Proctor doesn't go to church as often, and doesn't have his youngest son baptized by Parris. He struggles with the materialism not only of Parris, but also of other members of the town, and is disgusted with people's bickering and fighting.
Those are just a few things that Proctor struggles with; I hope that helps! Good luck!
In the meantime, he struggles to keep things off with Abby, and