YOU SAID:

i need to pee in myself

INTO JAPANESE

私は自分自身でおしっこをする必要があります

BACK INTO ENGLISH

I have to pee on my own

INTO JAPANESE

私は自分でおしっこをしなければならない

BACK INTO ENGLISH

I have to pee myself.

INTO JAPANESE

私は自分自身をおしっこする必要があります。

BACK INTO ENGLISH

I have to pee myself.