Dude! I just finished talking about this in another post but I'll re-iterate in here in case you miss it because it sounds like exactly what I have!
I just got back from having an ultra-sound on my right testicle, my symptoms were exactly the same as yours, pretty much no pain, one testicle getting larger but not hard lumpy style. I made an appointment with my doctor after trying to ignore it for like half a year, and he sent me for the ultra-sound.
Man I can't tell you what a relief it is to KNOW that you don't have cancer.
Turns out I have a cyst full of fluid at the bottom of my testicle. This is a perfectly normal thing to happen, in fact everyone has them on their nuts, most of them just don't grow!
My doctor said he has seen some bigger than grapefruits, so a little one is NOT a big deal, however it will require removal, be it a needle or surgery. My doctor said that the needle leaves the possibility that it will just fill with fluid again, so I will probably opt for the surgery.
Long story short, tell your parents. Come on, they brought you into this world and obviously care very much about you, so let 'em know what's going on! Remember you don't have to show them, but you will have to show your doctor and the person that does the ultra-sound. Mine was a lady and I thought it would be really awkward but actually we had a nice conversation. 😀
BTW what finally convinced me to get them checked out was I had a dream the night before I told my parents that I was dying of cancer. It was incredibly vivid and I believe it was a message. I know the boys are a very sensitive subject but THAT'S ALL THE MORE REASON TO WHIP EM OUT AND GET EM CHECKED MAN! Hope everything goes well.