Did your doctor get an electrocardiogram (EKG) done to rule out any cardiac problem? Your symptoms seem to be due to axillary/armpit lymph node involvement and less likely due to heart problem or cancer.
is disease with swollen/enlarged of lymph nodes which could be due to various infections or cancer.
Did you take full course of antibiotics as prescribed initially? If you stopped antibiotics as the pain went away, that can be a possible reason of getting the symptoms. This time, please continue with full course of antibiotics and then closely observe the symptoms. You can followup with your doctor to ensure that the lymphadenopathy is completely gone.
Wish you quick recovery!