Lump on left rib!!

Just wondered if anyone may help me. Since i was pregnant with my 3 year old i have noticed quite a largish lump on the bottom left rib. It has not grown in size at all but does cause some discomfort esp when i sleep on my stomach and now and again it feels like it is catching on my internal muscles (i know that sounds a bit dramatic). I remember having a very bad cough years ago and a very sharp pain in this same area when coughing once and was in agony; on the telephone to my doctor at the time he says i may have cracked a rib. I am just wondering if this could have been worsened by being pregnant i.e baby kicking etc and maybe scar tissue. i did get it checked out by a nurse who said the same and didnt really seem alarmed but im a little worries about it.
Can anyone advise if they have the same or know anybody who has the same. It is not necessarily sore but can feel a bit achy at times.
Thanks in advance for any help.

Loo x