I need info!

So I'm TTC and I am using an ovulation app. My last period was Dec 19th and lasted 8 days. According to my app, my fertility window was Dec 29th - Jan 3rd with Jan 2nd being my ovulation day. Also according to the app my next period comes Jan 16th. Now here comes the part where I need info, if conception has taken place, can I still take a pregnancy test 3-4 days before my upcoming period, even though it hasn't been 3 -4 weeks as needed for the preg hormones to build up for a home preg test ? Like everything is so close together, it's throwing me off. I don't know what to expect. Should I just go get a blood pregnancy test?.... help.