Is it obligatory to make up all prayers missed due to doubt concerning purity and urinary incontinence? And is there an expiation for making up prayers instead of performing them physically?

The questioner is not required to make up previous prayers or offer expiation because her prayer is valid as long as she is not certain that her ritual purity has been nullified or her clothes have become impure, for doubt does not affect certainty. If she becomes certain of the impurity of her clothes after the prayer, her prayer is valid and she does not need to repeat it. If she means that she masturbated or had a wet dream and did not perform ghusl (ritual bath), then she must repeat the prayers she performed before performing ghusl from janabah (major ritual impurity), bearing in mind that masturbation is forbidden.