How can one deal with the obsessive thoughts regarding ritual purity (tahara), fasting (including bleeding from the gums or wounds and phlegm), and nocturnal emissions, which cause psychological distress and affect daily life and acts of worship?

The cure for obsessive thoughts is to ignore them and not pay them any attention. Therefore, do not decide that your ritual purity has been invalidated, or that there is a barrier, or that you have had a wet dream, except with absolute certainty. As long as you do not intentionally swallow what you are certain is blood, your fast is valid. You may also act according to the opinion of those who hold that swallowing phlegm and mucus does not break the fast. Giving in to obsessive thoughts leads to great evil.