Im 13 and you have a small painful lump in your left arm pit but it comes and goes what is it?

I regularly had these as a teenager and sought medical advice as a result. They're almost certainly blocked pores or spots and will probably go down within a few days if you keep your armpits scrupulously clean - which I have no doubt you do, of course.

They ,ay also be boils, which sometimes vanish of their own accord - these can be prevented from returning by regularly washing your armpits with hot water. Don't squeeze them - boils can contain a lot of poison which could enter your bloodstream; go to the Doctor Who will drain them. However, they could be a sign of something more sinister including breast cancer (which affects people of all ages, including males) so, if they're still there in a few days, are an unusual colour or if they grow go and see your doctor as soon as possible.