Are wetness and a spot on the underwear considered urine, necessitating changing them and purifying the body, or is it obligatory to sniff to ascertain the smell of urine, especially with suffering from OCD and diabetes?

We ask God to cure you of whispers (waswas), and we advise you to ignore them and distract yourself from them, as this is one of the most important means to overcome them, after seeking God's help. The default state of your body and clothes is purity, unless you are certain that the stain is urine or other impurities, especially since you do not find the smell of urine, and given that you are afflicted with whispers (waswas).