Oh hon. You need even just a basic sex Ed course. When I was a kid, girls used to think you could get pregnant from sitting on a toilet seat. That is until grade 8 sex Ed. Please, please get informed on the basics.
I bet there is even reputable sex Ed courses on the net. Take one hon.
No, not from pee. Fresh semen from an ejaculation has to get in there. If you were four months pregnant you would have a long list of early signs other than a missing period. One missed period is not unusual. Four missed periods calls for a doctor checkup.