swollen left armpit

Last week I noticed my left armpit was swollen and slightly tender to the touch and when I raised my arm up. It is the entire axilla area that is swollen and I have found one tiny pea size bump in the upper back corner of my armpit that is tender to the touch. I saw my OBGYN and she felt it was due to some kind of infection and prescribed antibiotics. After 2 days on them the swelling had gone down and tenderness was gone. I was so relieved. Today, however, (the 3rd day on antibiotics) the swelling is back a bit and the tenderness is back although not as tender as before. This whole episode is scary to me because I had a (very small) squamous cell carcinoma skin cancer 13 months ago. Does the make sense that an infection would cause the swelling to go down after 2 days only to come back the 3rd day? I did have three places on my left arm from under the skin pimples that I had squeezed and were very red and tender. They got better on that second day of antibiotics and I felt that the swelling could have been due to them but why is it back today?? I would appreciate any thoughts or guidence as to anything I can do to further help this situation so I can stop worrying.
Thank You!!

[CCF-RN,MSN-JS]

Dear ALY11, Infection could cause swelling in the lymph nodes under the arm, and the swelling may fluctuate a bit as the body fights infection.  Keep your doctor posted as to how you are doing as you complete the course of antibiotics.