All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Know that the feelings that come to your mind are nothing but devil's insinuation. He (the devil) always tries to spoil your religion, faith and even your life. Therefore, be attentive and do not be a subject to such feelings. Seek refuge of Allah to protect you from Satan. Moreover, keep thinking about the creatures of Allah and work hard to get rid of bad feelings, and surely Allah will remove them.
For more benefit on evidence and signs of the existence of the Creator and the truthfulness of Prophet Muhammad, please refer to Fataawa ">22055, 389386, 347611, 81529, 389386, 85823, 85461 and 347611.
As for your first question about cheating in exams, please refer to Fatwa 81709.
For more benefit on the ruling on certificates and earnings if one cheated in exams, please refer to Fataawa 397198, 344719, 358828, 191489, 355567 and 362809.
Allah knows best.