I noticed the same kind of thing on top of my left testicle a few months ago. Because I already had testicular cancer on my right side, I was pretty worried about it and went to the doctor. They did an ultrasound and found that there was a small cyst on the epididymis on my left side. It's totally harmless and didn't require any treatment -- but it did freak me out a little bit.
Why not go to your family doctor and have them check it out? My guess is that yours is probably a cyst (or some other harmless thing) but then at least you'll know for sure and you won't have to worry about it anymore.
Hang in there!
28 years old
New York City, NY
Ultrasound on 1/23/12, I/O on 2/1/12
Classical seminoma, 4.5cm, RT invasion, LVI, no spermatic cord margin invasion.
CT scans clear
pre op bHCG: 57, post op: 2.4
Clear: 5/17/12, 8/23/12
11/29/12 -- CT scan shows 1 enlarged retroperitoneal lymph node 20mmx15mm, stage changed to IIA
12/17/12 - 3/17/13 -- EPx4 @ MSKCC
Clear: 3/7/13, 3/28/13, 5/2/13, more to come...