black or brown spot in upper thigh? how should i do? i am really crazy , it just like a big liver spot.

I noticed about a year ago that I had some light brown colour spots on my upper thigh area and at this time, it is like small space. .   They almost look like liver spots I think liver spots are occur more sunlight area but this one is in my thigh and i didn't expose with sun and i am now only 19 years old. Today I noticed there are more going down my upper thigh and some are bigger and more raised and takes a lot of space on my thigh.  All are basically the same colour.... and most are very small but because they seem to combine each other now like a brown big spot, I am so worry about that I did a search on Google ... but i cannot find it, they always said liver spot but all liver spots are happen in old people but i am young people and i was so sad, i cannot wear short pants, when i wear short pants this area is prominent and everybody think this girl is so dirty, but i am not. How should i do? I don't have age spots anywhere on my body ... except in this particular area so it makes me think it is NOT age spots.  Anyone know anything about these? These spot are not itchy and not like a ace and it is same with skin but the colour is brown. Please help me>>>>>>:( thanks u so much