Cyst??

[Little-miss-perfect]

Hi, can anyone give me advise please. I've noticed a hard lump (bit bigger than a pea) on the side of my boy, he's had it about a week & half, doesn't seem to bother him, my friend has looked and said it could be a cyst. Do cyst's last long? Luckly its about an inch away from the girth so it's not being rubbed.

Thanks