Pasting code into wordpress

When I get an affiliate code (which does have that affiliates web address by the way) and paste it into my website, the code changes as it enters my website address in the front of the code. I have even pasted the code in a text editor and then into my site. When I click on the link from a word I selected to insert to code, it takes me back to my website instead of the affiliate Link site. When I research the code it has my website in the front of the code.

Sorry to include so much but this is been an ongoing thing for the 4 days. I am stumped since I am new to wordpress.

I highlight the code, go to my editor, highlight a word,select insert link, update, then go to my website and select that word which is linked and it takes me back to my website per the code changing…(see below).

PLEASE HELP!

Thank you…..

(This is the current code)
<iframe style=”width:120px;height:240px;” marginwidth=”0″ marginheight=”0″ scrolling=”no” frameborder=”0″ src=”//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=exerc4you-20&marketplace=amazon&region=US&placement=1490540296&asins=1490540296&linkId=ZL5SRI76W7Y6S3PP&show_border=true&link_opens_in_new_window=true”>
</iframe>

(This is after I paste the code and update)
http://mywebsite.com/wp-admin/%3Ciframe%20style=%22width:120px;height:240px;%22%20marginwidth=%220%22%20marginheight=%220%22%20scrolling=%22no%22%20frameborder=%220%22%20src=%22//ws-na.amazon-adsystem.com/widgets/q?ServiceVersion=20070822&OneJS=1&Operation=GetAdHtml&MarketPlace=US&source=ac&ref=tf_til&ad_type=product_link&tracking_id=exerc4you-20&marketplace=amazon&region=US&placement=1490540296&asins=1490540296&linkId=ZL5SRI76W7Y6S3PP&show_border=true&link_opens_in_new_window=true%22%3E%20%3C/iframe%3E