The New Testament shows that true Christians can have moments of doubt, even about Jesus Christ. This is clear from when John the Baptist was imprisoned. John the Baptist had his doubts, so he sent messengers to ask Jesus Christ, “Are You the Expected One, or shall we look for someone else?” (Matthew 11:3). Jesus Christ understood that humans (even preachers) can have moments of weakness, so Christ sent reassurances to John the Baptist that He is the Divine Messiah. If you are a Christian who has moments of doubt, that does not necessarily mean that you are not truly born-again. It is possible for you as a human being to have moments of weakness. But the important thing is for you to seek reassurances from God as John the Baptist did and ask God to give you faith.