question!?

Right I have a lump on my right that has been there since tuesday. It is hard and seems to be getting bigger it's like the size of a pea. It was tender to touch on tuesday night, thats how I came across the lump, but there has been no pain lately. I started Microgynon 30 over a week ago and was wondering has the Microgynon brought this lump up? I went to my doctor and he has refferred me to a clinic to get a Mammogram but im only 17 and thought I was too young to get that done? People are saying I am and saying Im not? Has anyone had this before? Its really worrying me at the minute as my doctor was saying girls my age can get mastitis but when he was feeling my he said it was not mastitis as the it self was not lumpy. I am not on my period and am not due for a few weeks so I know the lump is not due to that. How long does it take to get an appointment at a clinic? Thanks to all in advance.