I don't think you will ever shake your baby. You mentioned other fears your suffer from that bother you, and it sure sounds like you suffer from a form of Obsessive Compulsive Disorder. Not the cleaning, hoarding, counting part (that's the compulsions), but the Obsessive Bad Thoughts part. I only say this because I have been struggling with it myself. I have always had O.C.D., but during pregnancy I started having terrible thoughts of harming others that I couldn't get out of my head, night or day. They were ridiculous things that I had never even thought about before! People who suffer from Obsessive Bad Thoughts NEVER carry out their obsessions, if they truly have this form of OCD. The reason they, and maybe you, have the thoughts is they can think of no worse thing than the thought they are having, and it bothers them so much because it is so unlike them. I had never had the obsessive thoughts until I was pregnant, and I believe the pregnancy hormones exacerbated the problem, and I haven't (cross my fingers) had those bad thought since my baby was born.
You can speak to your doctor about what you are thinking; they won't think you are crazy. MANY people, especially pregnant women and mothers, have gone through the same thing. They can prescribe anti-anxiety medication that will help. I bought a book called, "The Imp of the Mind" about Obsessive Thoughts that I would read to help me calm down. I put the link below. Let me know if you need anything!
If you aren't convinced that you have this, you could look around at some OCD sites and look under "Obsessive Bad Thoughts." If you find your fears are stuck in your head all the time and they won't go away no matter what you do or tell yourself, there's a good chance the cause is anxiety. I don't think most people actually think about shaking their baby before hand, it happens in the heat of the moment, and so I think it is just an irrational fear for you.
https://www.amazon.com/Imp-Mind-Exploring-Epidemic-Obsessive/dp/0452283078/ref=pd_sim_b_1