D.W.
Stress will def affect your ability to pump and you are probably feeling stressed about going back to work, trying to pump, needing to introduce a bottle, plus you aren't feeling well right now.
I had to pump exclusively for the 1st 12 weeks for my son. While I was learning to pump I found that if I relaxed and visualized my milk flowing and flood gates crashing open with milk my let down would start! Crazy as it sounds it worked.
Also, know that your supply is very well regulated at this point. You are making what you need while you are with him so your body isn't responding as well to the pump. But give yourself time to get well. And you will be pumping while you are away from baby so the milk will be there because baby won't be!
I don't think you need to make a full switch to formula. Why would you? You may need a bit till you get the working/pumping schedule going but full time switch? Nah! You like nursing, you are happy doing it so no reason to think you need to stop.
Ask your pediatrician for a formula recommendation. You will want something gentle as he is used to the gentle breastmilk. I highly recommend trying the Playtex nurser with the latex (brown) nipple. It is super soft like the breast.