Hi, I Noticed A Feeling A Couple Of Weeks Ago

Hi, I noticed a feeling a couple of weeks ago of a lump catching on my rib on the left hand side under my breast. I couldn't feel a lump externally at that point but have just found one. It feels soft and moves! If I cough or take a deep breath I have a feeling of it moving and it does hurt slightly at that time. Ordinarily it doesn't hurt at all. Hope this makes some sense? Difficult to describe. Any advice would be much appreciated. Thank you!