Is it obligatory to perform ghusl and cleanse everything that urine may have touched - including the bedding - if there is doubt about the presence of urine on the sanitary pad?

If someone finds a yellow spot on their garment and does not know its source, the preponderant view is to assume the original state, which is purity. Therefore, there is no need to wash the garment or bedding. Even if its impurity were assumed, doubt concerning the transfer of impurity does not lead to a ruling that it has transferred, because the default is purity. We ask Allah to cure you of waswasah (obsessive whispering), and we advise you to persist in supplication and humility, and to ignore these waswasah, while consulting a trustworthy psychiatrist.