"likely cancer at work"? There are lots of other reasons for weight loss. Are you eating your normal amount? The most likely cause is reduced eating from stress. Swollen glands for 18 years, maybe that's normal for you.
Moles do change as you get older but I assume you have shown them to a doctor. Are you seeing a doctor to know you have a low white blood cell count or is that something else you've had for 18 years?
I don't think melanomas turn up in more than one mole at a time.
Good luck.
If you don't mind sharing what are your counts?
Did they do a manual differential with your cbc count or a blood smear?
Do you have any night sweats, pain in glands while drinking alcohol, itching?