Late Period

I'm starting to panic a little bit... After being sexually abstinate for about a year (in the wake of a breakup), I finally jumped back into the mix. I am now about a week late according to Glow. My last period was about 3 days longer than average so I'm tying to keep that in mind, but it has still been 30 days. The first time I slept with the new guy was on the last day of my period (I thought it was over, but no such luck) and the second time was exactly a week later. I've avoided being intimate since because I'm paranoid. On top of the late period, I've been really sick for the past 4 days with the cold virus from hell. Intellectually I know that the chances of my being pregnant are really quite slim but I'm looking for your stories, please. 
For those of you with less than regular cycles, how long did it take for this app to start giving you accurate period predictions? How accurate are the fertility predictions?