sweat and najis

Dear brother i am very doubtful person. When i wash something i am confused or forget whether i have washed or not. I didnt wash some bit. What should i do in that situation.
Also brother is with sweat something became najis. Ie my underware is najis and i start to sweat does that make my thigh najis. If yes the other day i was taking shower and the cup touch my thigh whenni was wet. And then i touch the shower curtain. I wash the cup durine bath but i made havent touch and became najis. One thing is i dont know when i wash the cup in bath is my ghusal valid. But when i finish i wash the cup again. Becuase of my ocd should i ingorine if something is najis or not.