Why is it hard to get into teaching and even voluntary teaching assistant? I have a degree in the subject I would love to teach and yet I can't get into PGCE course or even be a volunteer in a school, WHY?:(

A great deal depends on supply and demand. There are thousands more certified teachers than there are jobs. Many people achieve certification but then go into another career so not every teacher will be in competition with you. If you live in an area with surplus teachers you may consider traveling to another town or even moving if you get hired out of town. I would recommend expanding your search area.