I bruise easily, have low fibrinogen, sometimes leg or arm aches, sometimes chest pain or palpitations, dizzy when i stand up. do i have leukaemia?

Easy to tell: Whoever checked your fibrinogen for whatever reason would have done a blood count. In leukemia at your age, this is always very abnormal, usually with bizarre cells. Without hard findings on physical exam, I suspect you are paying to much attention to the minor discomforts of ordinary life. Work hard, make friends, develop your abilities on a career path, stay cheerful