large lump behind right ear on neck

Hi I'm 19 and female... for a while now I've been very sick ive had chest kidney and stomach infections, theve all. Cleared (confermed by blood tests) however I noticed a large (bigger than a grape) lump behind my right ear its very painful (it feels soild) to touch and causes me to get sever headaches and ear aches. I also have the sensation of a lump in my throat and its hard to swallow I also find my breathing has changed (gotten slower) I've had a ct scan of the brain done to rule anything like that out and blood counts chest xrays etc have come bk perfectly normal..im just wondering if it could be something serious..although my doctor seems to think its not. What do you recommend??