Hi Sarah, I've lost over 180lbs now (about 50lbs of that on primal), so I know how you feel!
The honest truth for me is that I've not found exercise to be hugely helpful as far as the weight loss goes. It certainly helps with muscle tone and energy levels, but I've not noticed that it results in more weight loss than clean eating alone does.
That said, my approach was to find exercisey things that I enjoyed doing. Like hiking. So, the hubby and I started years ago by taking small little hikes. I think our first one was around a tiny lake near us, and I remember being so worn out after. Now we routinely do 15 mile hikes. We also love to explore cities. Just the other week, I walked from Union Square in San Francisco, wandered through Chinatown and North Beach, all the piers, the Palace of Fine Arts, down Crissy Field, over the Golden Gate Bridge, and into Sausalito. That's not something I could have ever imagined doing 180lbs ago.
Just find something you enjoy doing and your endurance will build. And if you make sure to eat cleanly along the way, every pound you lose will help you to have more endurance.