Ovulate straight after withdrawal bleed?

I stopped taking the pill on September 17 after only two tablets without a break from the pack before. My withdrawal bleed started 4 days later and finished after 4 days (so weds to sat). My body is probably all over the place.
Yesterday I felt sick and nauseous so I took an OPK just to check. It wasn't positive but definitely something there. Took another today and the line is lighter.
Is it possible I could have ovulated so soon after withdrawal bleed? And maybe had my surge in the night? 
These are the first OPKs I've taken so I'm new to all this! Thanks!