Re: lump behind ear?!
I'm not sure how much this will help you, but just for some reassurance. . . my mom had a lump behind her ear that bothered her on occasion - very much like yours. They told her it was simply a cyst and surgically removed it. She says that area of her neck still bothers her from time to time, but overall, everything is fine now.
If you don't have swollen lymph nodes, I would guess it's just a growth that shouldn't be there and that can be (and probably should be) removed. Sometimes a harmless growth or cyst can become harmful if left and allowed to grow. I would find a doctor that's willing to answer your questions and look for what the cause could be (or at least a suitable treatment if a cause can't be found) rather than shrug, write you a prescription for an antibiotic and send you on your way. If one is unwilling to do that, I would look for another. Good luck and I hope you find some answers soon!