Is there any open source alternative to MyHDL? I have started learning but finding it very difficult.
If you're planning to actually use it (e.g. to program an FPGA), GEZEL might be a good choice.
But if you're just starting out and only looking to learn, have a look at the first few chapters/projects of nand2tetris. They have a custom HDL which is easy to understand and introduced step by step.