Hi Cat! Sorry to hear things aren't going well for you.
Firstly, I would agree - talk to your doctor just to rule out anything serious being wrong. It could help greatly, and it certainly won't hurt. It will probably give you some peace of mind too.
Secondly, I don't think Ct5K had a built-in "easy week" but many learn to run programs do - essentially you drop back a bit for a week and pick up afterward. So perhaps try dopping back to week 7 or so? or wherever you feel comfortable, then picking things back up again. You don't necessarily have to drop back then climb back through the weeks as before, but sometimes taking it easy for a week can help you run stronger. By all means do some cross training activity in that "easy" week (such as swimming) but don't push it - it's supposed to be a rest. I'd not recommend leaving the running off completely though for more than a couple of weeks, unless your doctor recommends it or you've injured yourself.
And could you have injured something? That could sap your energy and willingness to run.
Personally, I'd take a week off, then do an easier week, then perhaps week 8 again. It's hard when you get into a program to stop and regroup, especially if you're worried about having the willpower to start up again. You've done so well so far, this will work out!