i did not see you in the chat.
my suggestions for you are as follows and based on the fact that you can actually feel something there under the rib. if you can feel something, something is there, and imaging studies are what is needed and they would include, depending on the exam your physician does....
1. an ultrasound of the area to see if a hernia can be identified or a soft tissue mass
2. a CT scan with contrast through the area
one or both of these would identify this lump or nodule, and depending on where it was located and other characteristics of the findings a surgeon might need to do a biopsy either with a fine needle or with a surgical procedure under anesthesia.
the left upper quadrant of the abdomen contains the stomach and spleen and this is also the lower portion of the rib cage so there's not too much here that is worrisome from my perspective, but a nodule or lump anywhere that is new and causing symptoms needs to be investigated and diagnosed. they are, occasionally, dangerous, and, occasionally, indicative of other problems which are not obvious from the symptoms.
I am standing by if you have any questions.