Hi! thanks for sharing your health concerns with HCM! Well, I ve gone through the details of your problem and can realize that the problem is a painless armpit lump with nausea, tiredness and loss of appetite! Anyways, if I were your treating doctor for this problem I would say that this is possibly not related to the stomach or polycythemia problem it could be something else like a lymphnode, a lipoma, neurofibroma or just a sebaceous cyst! There must be some kind of infection/inflammation in your body if this one is an enlarged lymph node but in other possibilities you need not worry! Therefore, you have to do an FNAC test of the lump for confirmation and to relieve your tension and also do not forget to revert back to us! wishing you good health!