Help with lag

I've played Terraria for a few years now, started off with the cracked version and in January bought the game off Steam, to really get the full experience. Problem is, it runs slower than the overweight kid in your gym class. I turned all the graphics settings to the least laggy versions (other than frame skip, I need that to sleep at night) but still lags like hell. I've played up to Plantera, but I thought about going to multiplayer, and it just breaks. Any tips to improve performance? Thanks in advance.