Making stupid mistakes 18 years later

I have been a NICU nurse for over 18 years. Just recently made a very stupid mistake. actually didnt make the mistake but didnt pick up on mistake made and am so upset over it. Micro premie, on triple antibiotics. On previous shift order written to d'c 2 of the antibiotics, picked up by nurse. These antibiotics should not have been d'cd. I took over patient, extremely busy, I wondered why meds were dc'd but didn't go any further with it. I always question everything, why I didn't this time; I just don't know what I was or wasn't thinking . When giving report to next shift , RN questioned me and asked Md and found it was a mistake. MD wrote wrong order, RN who picked it up should have known better and than me picking up patient on next shift should have definitely known better. And that is what is killing me, I knew better but didn't question it. Can't stop thinking about it. Just need to vent.