Feeling hopeful

Have been ttc since 2014 Jan and have been using this app since July 2015. My cycles have been 31 to 30 days alternating each month today was dat 31 and nothing .this month I did ovulation test for the first time and found out I ovulate late like day 20 or 21 so I assm hopeful that this is it. But since I put in ovulation tests in this app it pushed my expected period to the 28 th , this sounds weird. I took preg test on the 18th and it negative. Could I still be preg? Since my period is not here yet and normally is by now . Please help!