What Causes Lumps Under Armpits During Or After Menstrual Cycle?

Hello Ive been having these lumps come up under both armpits during or after my monthly cycle, however underneath my right armpit there are at least six lumps and maybe one or two that hurt a little. Ive had two allergic reactions this year as well and the lumps seemed to have worsened after experiencing these allergic reactions that leave hive on me for a very long time.