Among my many other issues, I am also a cancer-phobe. I never worried about illnesses or disease until the end of 2012 when I discovered a breast lump that the surgeon recommended removing. I was such a wreck, I could barely function, all I could do was lay around, cry, and imagine the worst until I got benign results/ Since then, I have bounced from scare to scare, some reasonable and in reaction to real symptoms, and others not so reasonable. I am also a new mom, just had my third baby, on Xmas day 2013.
Mine was not a planned pregnancy. The cancer fears did linger somewhat, but the pregnancy made me deemphasize my own issues. I also came to some zen about them, like if I did get cancer (oh, did I mention my armpit developed a giant lump at the beginning of the pregnancy and it still there today?), I felt like I would lick it and just do what I had to do to survive including chemo while pregnant (you can do that with some sorts of cancer), delivering early whatever.
What DID happen during my pregnancy is my phobia transferred to my pregnancy. I was terrified of Down Syndrome, I was fairly consumed with that possibility since we found a soft marker (but other testing indicated no Down Syndrome). I would say I did better with it that I did with my initial experience with health anxiety, like I was able to function and mostly dwell on my own time. I was also worried about rare things happening to her in the womb like getting fifths disease and, after birth, I freaked a little about whooping cough when my son got a cough. I am also fixating on some things on her skin (she has a mark on the back of her head that really bothers me). Melanoma is one of my triggers, and I have been transferring that fear to all three of my kids now. They are all going to the dermatologist next week, lol. I am also scared of things in the environment now that could possibly transmit to me or the kids. We just found a mouse problem, and hantavirus is the obsession du jour. I actually came on here to update my hantavirus post since we just finished cleaning the basement of mouse poo and hubby and I got into a huge flap over following CDC guidelines (I wanted to follow the guidelines, to be clear, haha, he thinks it's all ridiculous). I am disgressing here, but anyway. I don't know how you'll react but I think I kept it together in a satisfactory way during pregnancy and in my post partum period (my daughter is now 4 months)- not perfect but not debilitated by fear. The other thing that's really tough is the SIDS issue, and I had a momentary row with that but I wouldn't say I dwell (just check on her A LOT, although that's easing up).
You're right, no one can tell you what to do. But, I surprised myself with functioning semi-close to a normal human being that doesn't wake uo thinking about dying, haha. You might too. :-)