Praise be to Allaah.
We ask Allaah to grant you healing and well being always in your religious and worldly affairs.
What must be done when doing ghusl following janaabah is to make the water reach all areas of the body, including the area between the thighs. If you stand beneath the shower and the water reaches all parts of your body, and you rinse your mouth and nose, then you have done ghusl.
It is permissible to do wudoo’ washing each part of the body only once, but it is more perfect to wash each part three times, as is well known.
If you only wash each part once until you overcome this waswaas, there is nothing wrong with that in sha Allaah, and you should seek the help of Allaah by praying to Him (du’aa’) and asking for healing.
We ask Allaah to protect you and make you well. And Allaah knows best.