First BBT Chart..... Confused

Amanda • 24. Married since 4/14 expecting baby #1 March 2015!
Hi everyone! This is my first chart and I am just a bit confused. According to glow and another app I O on the 15th but didn't have a drop in temp till the 18th. I never had a positive opk so I just don't know what to think. My temp has risen since but just barely and not to anything really high. Any insight would be great!!!!