Hi Blu, welcome back it's been long time <3
I think that it can also be related to vitamin D if you are deficient. I don't know what low WBC count means but if it's showing a lowered immunity, then yes it can be related to low serum vitamin D levels.
I totally know how you feel, our minds tend to have catastrophic thoughts as fast as possible.
Doctor saying that as a possibility doesn't mean that it "is".
And you had a reason to lose weight, right? You tried to lose weight, it didn't happen by itself
Stay in now, take care.