Recently felt a little bump in armpit, a little bit hurt when pressed, no excretion or anything. What could that be?

Probably benign. Small infections and cysts of the skin under the armpit are common and not a cause for alarm. However if it keeps growing or is deeper than the skin (does it move when you move the skin?) it may represent a lymph node, and should be evaluated.
ARMPIT BUMP. This sound like a cyst or an infected cyst. Do see a dermatologist.