I have a lump on my left arm near the underarm. It's a little painful and when I raise my arm I feel something. It's 1cm in size. I just noticed this a few days ago. Do I need to worry or jut shrug it off?

Is it red and tender? If so you could have a boil. Take a warm washclothe and do compresses on it. If it doesn't go away then you might need to be seen. It could also be a clogged pore. Most pores get clogged by your underarm deoderant. You need to see if your deoderant has aluminum in the ingerdiants if so try switching to something different.