Is this thing cancer or what

This is my third post. I guess if I don't use the right words in the subject no one looks at the post. Any way.......I have a pea sized lump on my right teste but here is the weird thing. It disappears until I agitate the area where it was and then within about 2 minutes the lump swells up to size and after I leave it for like 30 minutes it shrinks back down to almost the size of a pin head. If it is a cyst; A) will it make me infertile? AND B) can a cyst be cancerous? I notice a very dull ache in the right side of my back and testicle. It also feels kind of heavier. I'm almost convinced that the whole testicle itself swells up as well. It is on the larger testicle which happens to be about twice the size if the left one and it does hang lower too. It seems that no one else has a lump that changes sizes like that on the entire interweb so I am hoping someone here can help me. Thanks