You are both right about the stress.
A long time ago, I was having period problems, and my doctor said that it was because I hadn't ovulated. I was studying for finals at the time, so I asked the doctor if the stress could have made me not ovulate, and he said yes.
So stress, including stressing about not getting pregant, will stop you from ovulating.
I guess it makes sense from an evolutionary perspective, in primitive times if you were in a stressful environment, maybe because there wasn't enough food to eat or you were in a situation where your life was constantly in danger, it wouldn't be safe for you to be pregnant at that time.