It's normal for grief to fluctuate.
There are normal stages: shock, denial, bargaining, anger, grief and finally acceptance combined with peace.
These stages can happen at different times, they can overlap, disappear and return, and there is no definite or normal amount of time.
Sometimes grief can be complicated because there was conflict in the relationship. This means there's lots of unresolved anger hanging around in the person left behind, and with no target to focus on, it can turn inwards.
If we have a strong sense of duty, and believe that we didn't for our best for that person (there were probably very good reasons), we can end up feeling guilt and being unwilling to forgive ourselves. In a case like that we get trapped by guilt. It's a form of self-punishment which can be extremely cruel and unjust.
It is okay to let go of guilt and to forgive yourself.
If you want to talk further about it, you can message me.
I was trained as a Lifeline telephone counselor.