Bump Is Enlarging And Twitching Is Scaring Me Now

It seems that the bump on my head is enlarging and now i'm really scared it's a tumor. This bump has been where i've had headaches originate and i've gone to a doctor but it was just a young doctor in training and I told him all about it, and he said if it gets bigger than call me. I really hate it that he didn't take action about this, everyone seems to ignore me when I say I might have a tumor, they say i'm delusional sometimes. There has been little twitches near this lump. So, how would I go about seeing to get an mri scan or something. I don't think my medical coverage covers this kind of thing so please I really need to do something that I should of done years ago.

I'm 20 year old guy, average weight and very healthy.