What is a hamtologist/oncologis? Why do I need to see one?

A hematologist/oncologist is someone who specializes in blood disorders and cancer. The reason you need to see one is because you have altered blood levels that suggest problems that your regular doc can't find. Since you mentioned being tired, dizzy and bruising it may be more than just anemia that is causing your problems which is why you are seeing a specialist. Yes it could be something serious but until you see the doc try to think positive. One possibility is cancer but it could well be something else so do NOT jump to any conclusions until you see the doc. Just get your appointment set up and be very thankful that you are getting seen and getting whatever is causing your problems diagnosed finally.