On the days of the month when I am excused from praying and fasting, my imaan drops so much that by the end of the cycle I end up committing some major sins, then the next few days I feel extremely depressed, please advice me with a solution to this problem بارك الله فيك.

Recite the Quran from your memorization, turn to the qibla, make dua, raise your hands, make a lot of dhikr, and attend many lessons so that you occupy your time with obedience to Allah. At the time when you are excused, it does not mean that you detach from the means that increase your piety, causing your piety and iman to decrease, and then you start falling into sins. What you should be doing, especially at these times, is to be careful to increase in dhikr and in the acts of worship that you are capable of doing. Also, surround yourself with those who will encourage you to do better, not to fall into sin, as the environment plays a huge role in it.