Progress tends to unearth new problems, thoughts, and doubts. Of course it does. This is within the nature of moving into new territories, accomplishing new feats, expanding your comfort zone. Be aware of these new doubts.
However, know that these are tactics that the adversary uses when he sees we are making progress. He will do all he can to stop us from progressing, to have us become lukewarm in our beliefs, confidence, and effort.
Don't ever cool down, my brethren. Keep the gospel flame burning. Keep your testimony. Keep progressing. Keep the faith.