All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The solution for this problem, according to the texts in the Quran and the Sunnah, is to ignore these whispers, repel them and not to pay attention to them. You do not have to wash your body after urinating. Rather, it is not legislated for you to wash any part of your body except the area of impurity. It is not legislated for you to wash any part that you doubt whether or not impurity has touched it.
It is impossible for urine to reach the arms and the legs, let alone the head. These are all whispers from the devil which he casts in order to spoil your life and make it miserable.
The issue of Ghusl (ritual bath) is easy, and all you have to do is pour water over your body until you feel that you have predominantly covered it all. This is how you purify your body and achieve purity, and it should not take more than few minutes for those who are afflicted with whispers.
Therefore, the mission that you need to focus on and the battle that you must fight is against these whispers. You should ignore them and not give in to them, while seeking the help of Allah and asking His support in order to achieve this goal.
You can reads some of the advisories we have on our site on this issue. We ask Allah to cure you.
Allah knows best.