Dear Todd, 

You have to be able to tell the difference between fear, questions, humility and doubt. When we bunch them together we can get confused, and much also depends on how we react to them. 

It is quite healthy to fear the priesthood. It is absolutely necessary to know that we are not worthy of it - not just to say we know, but in our heart of hearts to be convinced that if it were not for God's grace and call it would be presumptuous for us to take it upon ourselves, and impossible for us to persevere in our commitment as priests. 

As regards doubts, we have to distinguish and reflect further. Some doubts may certainly be God speaking to us and leading us elsewhere, and other doubts may be no more than temptations. 

Seminary is a time of discernment. Some discernment has to have taken place before you joined the seminary, but in the seminary itself there is further discernment to be done. The bishop through his representatives has to discern if you truly are called since he is the one who will receive and ordain you for the Church, and you have to reach the deep, internal conviction of your own vocation and learn to base your life on a set of habits, dispositions and practices that will help you persevere in your call.  

Let us look first of all at some things you cannot doubt: God calls some men to be priests. When he calls them they still are men, with the weakness that is inherent to being a man, he does not turn them into angels. Priesthood always entails sacrifice. It is necessary that there be priests. You are in the seminary. Christ's enemy is always going to try to entice you away from what God wants. Grace exists, it builds on nature but does not substitute for nature. 

You cannot resolve your doubts on your own. When confronting them you need to ask for outside help, in the form of your spiritual director. He is in a better position than you to ask the proper questions and help you reflect, and at some stage to give you an honest opinion whether your doubts are the usual temptations or sign of something else. And once your doubts are cleared up you have to realize that if the same ones surface again they are most probably temptations. 

Meanwhile, give yourself heart and soul to Christ in your prayer and seminary duties, and be absolutely confident that he will lead you and take care of you. 

God bless.