HI chickie (may I call you that?)
I want to assure you this is not odd. While it does seem that you have some rituals around the anniversary, something in this works out the grief for you. I hope the look your therapist gave was more of interest in this news

not that you are a freak - you are NOT!
I had an odd grieving situation around my mother...a hardcore alcoholic who was institutionalized in 1991 after her last binge. She died 2008. In those years, out of the blue, I'd find myself grieving the loss of her while she was still alive (but unreachable due to the brain damage). I learned to let it come and it would - doing the dishes (my partner loved those times...he'd walk out of the kitchen and return to find my in tears scrubbing the pots), seeing a woman who resembled her at the store. I'd usually cry & nap afterwards.
There were no rulebooks, only instinct.
And even now, writing about her, the grief is keen. I always think grieving is cleansing. For me, feeling the grief keeps depression at bay. The depression seems to have no home. Sure, it's a downer, but somehow that is not my experience of depression. I hope it is the same for you.
For the first time this year, Mother's Day & her birthday were not grief triggers for me. So I can tell you things do change, and I hope you can talk about this more with your therapist.
Stephen