Hello and welcome to HCM.
Thank you for your query.
Yes, it is common for a few of your
lymph nodes, especially the ones in your axillary region (armpits) to get slightly swollen around and during your period. This is due to an effect of the hormones, which also cause slight breast enlargement during your periods.
If your doctor has found this to be a
cyst, you will have to analyse this further. As a cyst could be a result of infections or even cancer. But, in my opinion, if this swelling comes and goes at/around your period, it cannot be a cyst, and is related to a change in your hormone levels, which occurs during
menstruation.
I hope I have succeeded in providing the information you were looking for. Please feel free to write back to me for any further clarifications. I would gladly help you.
Best wishes.