I think stress and conception are linked in ways they should not be. The idea that women should "just relax so they can get pregnant" puts all the "blame" for infertility on the woman. Everyone can probably name 1 or 2 women they know who got pregnant when they started to relax, but that's because it's so rare, it's notable. The vast majority of women get pregnant doing what they normally do - have jobs, run around chasing kids, caring for older parents, juggling life's stresses. There are lots of reasons why some women don't get pregnant when they want to, but working at a job is rarely that high on the list.
If a job was so stressful that you weren't eating reasonable meals and getting reasonable sleep, or if it made you too distracted to take any medications the doctor recommended, that would be another story. But still, anything could be a distraction in those cases.
I would think that quitting a job would bring more stress - you wouldn't have the income, and you would sit around the house focusing entirely on whether you are ovulating, having sex at the right moment, and whether it's too soon to try another urine test.
But no one here can tell you what to do. You need to look at your entire financial picture (including medical benefits), talk to your husband/partner, discuss with your doctor, decide why you are so anxious about getting pregnant, and look at other options to calm yourself. (I realize you want to and that you've had some disappointments - but are you creating more stress? What else can you do for that? Massage? Relaxation tapes? Counseling?) You need to have a plan in case you quit your job and then don't get pregnant in 3 or 6 or 9 months. What will you do then? Will that be less stress than your job and income?