Must I be overly fearful regarding the soundness of my fast and search for fatwas, or should I stop this line of thinking and cease this whisper (waswas), and how can I rid myself of the whisperings (waswas) concerning the invalidation of the fast?

Being keen on the soundness of worship is good, but if it reaches the level of obsessive doubt (waswasa), it is blameworthy and should be avoided. To learn how to get rid of obsessive doubt, please refer to Fatwa No. 59951. Among the things that dispel obsessive doubt is learning the rulings of Sharia. The things that invalidate fasting and break it are known and have been clarified by scholars. If you encompass them, the problem will disappear. Therefore, you must seek knowledge.