When would i ovulate?

C
I'm on CD7 and my period ended today. Glow is saying my fertile window starts in 2 days. For some reason I feel like that's not right? Lol. I would use OPKs but I really don't want to spend the money on them. 
This is my first period since I found out I was pregnant with my son (2 years ago). Is it hard to know when I ovulate if this is my first period since then?