Blister between the breasts

Hi. 21 year old and I have a blister like growth between my breasts. Its not under thin skin like a burn blister would be, but its thicker skin. I don't know what it is from. I know I didn't get a sun burn or just burn myself. I feel something like a knot under it though. I'm kinda of worried about it though because I just had a cyst removed from my tailbone. Do you think its something serious?