What Causes Lumps On The Testicles?

I have recently felt a small lump, around the size of a pea, on my left testicle, and at the bottom to under side of it. It does not seem to be on my testicle exactly. I also have this other lump on that same testicle, which is on the upper left side of it. I went to the doctor to have the lump on the upper left side, and they said it was their opinion that it was nothing to worry about. They did not do an ultrasound for that lump. So I am wondering if this other lump could be related to the one that I have on the upper left side. It seems like the one on the upper left side is a cyst, and I am wondering if the one at the bottom could be a part of that cyst that I seem to already have, or could it be testicular cancer. To me, it does not seem that the one at the bottom left is attached itself to the testicle. I plan on going to a urologist to have it checked out.