Testicular cancer/lumps, pains.?

Okay so I had a lump about a year and a half ago and went to he doctor who said it would ne nothing to worry about but as i was 16 it will be checked out anyway, I went to the hospital where it was scanned with one of those devices (the name has slipped my mind) that they use to do an ultra sonogram... the doctor almost wasn;t taking me seriously and didn't seem like he scanned all the way round but i thought he must be doing it right. A year later I went back to my doctor (not to have a scan) as one testicle is quite bigger than the other, and mildly painful when checking for lumps etc he again said he didn't think it was anything Is it natural for one to be bigger than the other and the lump hurts a bit but they said it was something tissue like i forgot, and is it natural for it to hurt when examined/checked?