Walking sometimes feels like I'm climbing Mt Everist

I don't know what has happened in the last few weeks, but I'm getting really, really slow. Walking has become like climbing a hill.  A steep hill.  I just went on a walk with my friend and our kids.  I thought for sure I was going to die.  That's not like me at all.  Exercise has been my saving grace through this pregnancy.  And it's always been relatively easy up until now.  But just thinking about it makes me feel extremely tired.  Ugh.  I hate this.  I'm ready for my body and energy to be back up.  

I have no plans to stop.  But I'm going to have to pace myself and slow down.  

 Must. Keep. Going.  

Perhaps today my resolve was down a bit by my children constantly whining throughout the entire walk.  

"Can we get out?"  No.  *Burst into tears* 

 "Are we going to the park?"  No.  *Burst into tears*  

"Why is the pavement cracked?"  I don't know.  *Burst into tears*

Over and over and over.  

By the end I was about to burst into tears.  I'm not going on a walk again with my kids until this baby is out.  Pushing that double jogging stroller while enduring constant whine is enough to make me drop the kids off at Good Will and pray for the best.  "I'm going to sell you to the gypsies" as my dad used to tell us.  

I will, however, keep walking alone.  MWF I can do that- as the kids are both in school.  I need to shoot for morning too because by afternoon I'm just done.  

It's been a really rough day physically.