All of us (even the saints) have times when we have difficulties with some aspect of our faith. When we voluntarily yield to these, it is sinful. When we struggle against these difficulties, it is courageous and meritorious. It is OK (it is good) to seek understanding to confirm and strengthen our faith.
Some articles from the* Catechism of the Catholic Church *which may help you (emphasis added):
157 Faith is certain. It is more certain than all human knowledge because it is founded on the very word of God who cannot lie. To be sure, revealed truths can seem obscure to human reason and experience, but "the certainty that the divine light gives is greater than that which the light of natural reason gives."31 **“Ten thousand difficulties do not make one doubt.”**32 158 “Faith seeks understanding”:33 it is intrinsic to faith that a believer desires to know better the One in whom he has put his faith, and to understand better what He has revealed; a more penetrating knowledge will in turn call forth a greater faith, increasingly set afire by love. The grace of faith opens "the eyes of your hearts"34 to a lively understanding of the contents of Revelation: that is, of the totality of God’s plan and the mysteries of faith, of their connection with each other and with Christ, the center of the revealed mystery. "The same Holy Spirit constantly perfects faith by his gifts, so that Revelation may be more and more profoundly understood."35 In the words of St. Augustine, "I believe, in order to understand; and I understand, the better to believe."36 164 Now, however, “we walk by faith, not by sight”;49 we perceive God as “in a mirror, dimly” and only “in part”.50 Even though enlightened by him in whom it believes, faith is often lived in darkness and can be put to the test. The world we live in often seems very far from the one promised us by faith. Our experiences of evil and suffering, injustice and death, seem to contradict the Good News; they can shake our faith and become a temptation against it.
**165 **It is then we must turn to the witnesses of faith: to Abraham, who “in hope… believed against hope”;51 to the Virgin Mary, who, in “her pilgrimage of faith”, walked into the "night of faith"52 in sharing the darkness of her son’s suffering and death; and to so many others: "Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with perseverance the race that is set before us, looking to Jesus the pioneer and perfecter of our faith."53
2087 Our moral life has its source in faith in God who reveals his love to us. St. Paul speaks of the "obedience of faith"9 as our first obligation. He shows that “ignorance of God” is the principle and explanation of all moral deviations.10 Our duty toward God is to believe in him and to bear witness to him. **2088 **The first commandment requires us to nourish and protect our faith with prudence and vigilance, and to reject everything that is opposed to it. There are various ways of sinning against faith: Voluntary doubt about the faith disregards or refuses to hold as true what God has revealed and the Church proposes for belief. Involuntary doubt refers to hesitation in believing, difficulty in overcoming objections connected with the faith, or also anxiety aroused by its obscurity. If deliberately cultivated doubt can lead to spiritual blindness. 2089 Incredulity is the neglect of revealed truth or the willful refusal to assent to it. "Heresy is the obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith, or it is likewise an obstinate doubt concerning the same; apostasy is the total repudiation of the Christian faith; schism is the refusal of submission to the Roman Pontiff or of communion with the members of the Church subject to him."11The words I highlighted above — “Ten thousand difficulties do not make one doubt” (quoted from John Henry Cardinal Newman) — were spoken to me once by my confessor when I thought I was having doubts about my faith, and I found them very comforting. He explained that I was experiencing difficulties, not real doubt. I had not rejected an article of faith, but was grappling with some things that I did not understand.