HUGS
I have lost 6 of my own piggies this year, most of them older ones and all of them to different causes. The first couple of deaths happened within a week of each other and neither was one I could brace for (one was an emergency fast growing mammary tumor op on a younger piggy that turned out had a very irregular heartbeat and who sadly didn't make it; she'd gone within 24 hours of me noticing that something wasn't right; the other within 48 hours).
Like you, I have been feeling very low and inadequate at times and very jittery whenever a new issue has arisen with yet another piggy, especially after my third trip in a row to the vets for pts - even though I
know that I did the right thing each time and that there is nothing more I could have done for any of the piggies.
Your experience is very normal for your situation, as you have to go through yet another grieving process before you have finished the previous one and your coping mechanism is currently running on overload/high alert.
You will get over it as time passes and nothing bad happens and you can slowly digest it all. Unfortunately, when you have a larger number of pets, they are a lot like British buses - nothing for a long time and then several all at once.