Hickey-like mark on my bum!

What could this be?  Is it worth a trip to the doctor?  I have a hickey-like lesion right in the middle of one cheek on my bum.  And no it's not a hickey or bruise...it's been there for at least 4 months without much change (may have gotten a little darker and drier). It is dime-sized, smooth, just slightly raised (kind of like a little swelling under the skin), a little dry, feels kind of like a bruise when pressed, does not itch or anything.  Don't think it is ringworm...tried lotrimin and no change.  I am in my mid-twenties and have no health problems (other than this wierd thing on my bum).  Any ideas?