Mah dear, I think you're starting to get what all nurses, doctors, and scientists get after awhile due to all of their knowledge - you're becoming a pathogen-phobe!
As a nurse, you know what sanitary practices you need to keep in order to protect not only yourself, but others. Be confident in your knowledge.
Since you are a nurse, what do you think you should be doing each year...since 2009? Flu shot!
You got them before you were pregnant and nothing happened. What changed? What stopped you from continuing to get them? Go get it each year! Give yourself that added layer of comfort that and get yourself that flu shot each year.
Also, one more...again, since you're a nurse...you also know that the chances of the flu killing you right now are what??? Slim to none? What kind of condition do you need to be in for the flu to kill you? Severely immunosuppressed, elderly, other confounding illnesses such as cancer, etc.
So you KNOW very well that your thoughts aren't rational and that you are just fine. Remember your knowledge, remember your training, pick up your head, smile, and go get your flu shot.