Today I noticed a small lump in my armpit and when I squeezed it, a little white pus oozed out and it pained a little. In the same armpit, I also have lymph nodes which stay a little bulged/swollen normally and pains a little a few days before period (during PMS). These have always been there since I remember but this new small lump under the skin is new. Please suggest what could be causing this and is it a reason to worry.