Hodgkin's Lymphoma and SCT Survivor Low Platelets

I'm a Hodgkin's Lymphoma survivor and have been in remission for about 5 years. I recently noticed a few bruises on both arms and one of my legs. I have been feeling fatigue and worn down, so I went to urgent care this weekend. They told me my platelets were 25,000. Back in September, they were 96,000.

I've been reading about what can cause this besides a virus, another blood cancer, an immune problem and B12 deficiency. I'm a vegan, never eat meat, cheese and milk. Since September, I dropped dairy products and went from vegetarian to vegan. I am hoping it's a b12 deficiency that has caused my platelets to dive down to 25,000.

Has anyone been told that their low platelets were caused by a B-12 deficiency because of a vegan diet? I am getting more blood tests and a bone marrow biopsy this week. I am hoping it's a diet deficiency. If it is, I have no problem switching to a diet consisting of yogurt and cheese. I should know more this week, but would like to touch base with others having this issue.

Another question has anyone with prior Lymphoma and a stem cell transplant been diagnosed with Leukemia?

Thanks for any info.