How much of that memory is in use before you load a game? If you have 3 GB in your system and you're using 2.9 GB of it before you load a game, not many recent games are going to run well. You may be able to get games to run fine just by shutting down unnecessary bloatware that is running on your computer for no good reason.

What do you have for a computer anyway, to only have 3 GB of memory? The modern standard is DDR4 and has been for a few years, and they don't even make DDR4 modules smaller than 4 GB.