Pain and lump in left breast

Hi everyone. I have a 17 month old baby boy and am still breastfeeding. I started experiencing some pain in the lower part of my left breast about two days ago. The pain is just under the breast and it hurts when pressure is applied to it. There is no pain when my son breast feeds and milk flow seems normal. It’s just really soar and when I examined it further I noticed there’s what feels like a lump. We’re scheduled for an appointment with our doctor on Thursday. Is there any one who has had a similar thing happen to them? Other than this and a blocked milk duct when my son was s month old, I’ve had no other issues with my breasts till now. Any advice or help would be much appreciated. Thank you advance

#update

Thankfully the mammogram showed no cancerous lumps. The doctor told me that it’s probably hormones causing the pain and the lump appeared to be milk. If any of you ladies ever experience the same thing please get it checked out. My doctor advised me to come in for a mammogram once a year and to do self checks as well just after my period, when the breasts are still soft and tender and lumps can easily be located. Self care is important ladies and I had to learn the hard way with this scare.