Crashing after starting the game and joining a server.

As of yesterday, my game has been crashing unexpectedly whilst in the middle of playing the game. There's no lag or anything else open to slow down my computer's performance. I can open worlds and play on servers smoothly, but after only 30 seconds to a minute of playing, the game just suddenly closes and shows a message that an error has occurred and the game has crashed. I can also use mods, resource packs, and shaders just fine, and they're ones I've always used, but after a couple minutes of playing it continued to crash for no reason. I figured something was up with them, so I took them out of their folders and switched to normal unmodded Minecraft; however, it still crashed, if not, got even worse, and gameplay started to only last a minute. I know it's not my mods messing up the program, everything is up-to-date (Java and the computer itself), and my .minecraft files haven't been altered in any way. I have also used a virus cleaner, but that didn't help much either.