My testicles feel kinda hard. Is this a problem?

About a year ago, my left testicle started to swell up. I didn't know what was happening and I thought this was normal but as the day went by, it grew bigger and I stated to some pain. A day later it went to it's original size but the testical got kinda hard. it then happen to my right testicle but not as bad as the left. I noticed that my sperm looked different from before. It kind of sinked to the bottom instead of floating like it use to. I use to wear tight briefs and Im not sure if that was the cause of it. now my testicles feel kind of harder than they use to feel. Is this something serious I should be worring about? I also kinda feel like if something inside were tangled. Like if the tubes were the sperm travels was clott. Is it just me or i'm I imagining this?