I'm fed up of this!

For 2 and a half months I've feared having malignant melanoma, as I have a mole on the back of my neck! I first started fearing it when I saw something about skin cancer on the news, over the summer, since then every little thing I've felt on my neck has had my breakdown in fear and anger, any little sensation in my neck! I've researched symptoms myself, none of which I realise I've actually had, but at the time I thought I had, I even spoken to a dermatologist, who checked it out, talked to me, and din't diagnose me with malignant melanoma, but actually suggested stress was bringing on the fear, and I've since realised I've got hypochondria, and even though now I know I haven't got this form cancer, I still worry about it! I've had enough! It's effecting me in every walk of life, I'm not myself, I'm quiet I'm out of character, and I just feel these past three months of my life have been a waste! HELP!