No appetite, frequent infections, can't seem to take satisfying breath, bruising easily.... No tiredness or body pains.... Leukemia?

Hard to say... Leukemia can present with multiple signs and symptoms including but not limited to: bone pain, refusal to bear weight, gum bleeding, bleeding from other sites, pallor, lack of appetite, fever, night sweats, unexplained weight loss, easy bruising, fatigue, multiple infections, etc. If a concern for leukemia exists, consultation with the primary care physician or a hematologist is recommended.
Don't self-diagnose. Before you guess, have a good full exam. If you have a problem with depression, thinking about dire medical conditions will only make you feel worse. Work with your therapist and doctors to evaluate the symptoms and it might be much less awful. Something is wrong and hopefully it can be resolved. Hope it goes well.