I have abig lump under both my armpits probably the size of a lemon, no pain just uncomfortable because its so big i've had these since i was 15 yrs ?

Lipoma: Most likely you have is a lipoma ( a mass of fat ). It could also potentially be mammary tissue. It can be removed surgically.

Breast Tissue: Lumps in the armpit can be lots of different things, best sorted out by a surgeon. However, if these lumps have been present that long (unchanged) & are the consistency of fat and/or breast tissue, it sounds like ectopic axillary breast tissue. This is merely a variation of normal and no clinical consequence. If it bothers you, surgical excision can be done.