From the look of things you seem to be suffering from a coronary artery diseases (heart condition) known as unstable angina
with all the risk factors you present ( of blood disorders and cancer). Another possibility is cardiac or lung metastasis
from your cancer (depending on which organ was affected). I recommend that you do a chest x-ray, MRI, CT scan
and to consult a cardiologist
or an internist. Pain can only properly be managed if the cause is known as it might require palliative care
If the cause for the pain is simply unstable angina then appropriate medication (s) will be prescribed by your cardiologist.
Hope this helps and wish you a better health