From what you describe it seems like the ingrown hairs have been causing the infection in the hair follicle called the folliculitis
.Which can cause the enlargement of the lymph
nodes in the arm pit.This can present as lump in the armpit.Well, there are other conditions like "Hidradenitis
Suppurativa"which can also present with similar signs and symptoms.I suggest you consult your dermatologist
at the earliest and take appropriate treatment.