Thanks for the question.
This doubt you have is common. It is diabolically inspired, however, because the demonic forces want to discourage you. When we hear the voice of the accuser, he tells us we are not worthy, we are not sincere, we are not doing God's will, we are useless. This game of discouragement is meant to wear us down and get us to throw in the towel. The fact that you have these doubts means that you are in fact doing good and the devil wants you to stop. Every saint in the making has had to fight these battles and for us it is no different.
The trick is to imitate the saints, who never felt worthy or good enough but nonetheless kept pushing onward. We must behave as though we are sincere even when we don't feel like it. It's like faking it until you make it.
Remember the man who said to Jesus out of his recognition of his own weak faith:
"Lord I believe, help my unbelief." (Mark 9:24)
We must do likewise. If you feel insincere, pray to become more sincere. Don't assume that your simply stuck and cannot move forward. God will help you move, but He will do it on His Terms. There may be lessons for you to learn at this level — like how to trust that God will get you to the next point. Each step is a dying and rising that will bring you down low to see your helplessness, only to rise better in the strength of God. Don't despair about the pain involved, just roll with it and unite everything to Jesus through Mary.
Lastly, I would read something like St. John of the Cross (readings) or St. Catherine of Siena (readings) to witness how the journey to God takes us through many different stages, but ultimately, in the end, brings us to joy!