Issue with html coding

I am having a heap of issue with using html to code my pages. Firstly, (particularly when i insert a youtube video) wordpress seems to reconfigure my coding…… I end up having new code made, which screws up the entire page.

This is also happening with new tags being created everywhere…. I scroll down to find a constant amount of repeated tags or just wasted tags. I have gone through a number of times and cleaned it out, but they eventually keep coming back -.-

I have hit the point of frustration lol and decided to post in support, any help on this issue would be greatly appreciated.