Will God forgive a young man afflicted with OCD who doubts creed and curses to himself without uttering it, and who fears that he will not be forgiven?

Dismiss the whispers and pay them no mind, for indulging them leads to a great evil. When you pray, do not repeat words or verses. Waswas in matters of creed does not harm you nor expels you from Islam, as long as they are mere psychological thoughts, and Allah has forgiven this Ummah for what its souls whisper to them. Continue to strive against these whispers and endeavor to rid yourself of them, for your dislike and aversion to them are proof of the soundness of your faith. Seek Allah's help in repelling these whispers.