Why do my testicles hurt?

I've been having pain on my testicles for a while now. I tried ignoring it, which isn't always a good idea. They hurt sometimes when i have intercourse. I was thinking maybe it's because I sometimes have too much sex. Also, they seem to move too. The pain seems to be under neath my testicles and the little tubes. Can anybody tell me why it might be? I'm really worried and don't know what to do. I'm worried it might be testicle cancer :/