Just a question...

So after having a baby your at higher chance of falling pregnant again/more fertile? 
If you are breast feeding exclusively does that lower your fertilty levels? Do you still ovulate when exclusivly breast feeding? 
I'm guessing if your ovulating periods will resume? 
If someone is exclusivly breastfeeding  no periods happening would a suggestion to take a pregnancy test every so often or would that be pointless? 
Thank you in advance