How Possible is it?

It's going on 5 weeks since my last period and me and my partner had sex the entire time I got off my period my period is usually normal and it was due last week. I took a home test 3 days after a missed period and the test was negative. How possible is it that I'm pregnant and when can I do a ultrasound to see if I am or not and when should I take another pee test?