I had un protected sex on Wednesday last week started my period
The day after so Thursday. He came in me once while on peeiid
And now its been a week as of today. Hes 42 I'm 21. Is there
A chance I'm pregnant?

Slim, some women can get pregnant the day before, some even on period.

You will have to wait till next month ( really no other choice) and see if you have or miss that period. Then if you miss it, a week latter you try a test