Lump in armpit

I am seriously so worried it’s making me sick...

I have breastfed both my babies and I recently just breastfeeding my youngest. My armpit looks swollen. When he was first born I had an ultrasound and everything looked fine. They didn’t do a biopsy because the little lump inside was so small. They said it would go down after breastfeeding and it hasn’t. Should I go in and be seen I am so scared it’s cancer and I have been feeling so sick lately. I don’t have any lumps in my boobs