What should I do if, during prayer, I suspect that I did not cleanse myself properly after relieving myself and performing ablution? Should I interrupt it to check, or should I complete it and then check?

One must continue praying and not interrupt the prayer due to doubt about purification (Istinja’). The default assumption is that it is valid until proven otherwise, and prayer is not invalidated by doubt concerning what nullifies it. There is no need to verify purification after the prayer, as it is presumed valid until proven otherwise. One must be wary of obsessive whispering (waswasah).