HELP PLEASE! Excel sizing issue!

Hi everyone,

First time using this forum so I hope I am doing the right thing!

I have created a finance spreadsheet that has a few macros, some fairly (ish) lengthy formulas in it (SUMIFS etc) and conditional formatting in it. It really is not massive or complex! I have made spreadsheets with more in them than this and never had this problem, but...

Last night I added a few columns and formulas etc for something new and then when I saved the file, it took forever! The file size seems to have gone from something like 350kb to nearly 20,000kb! It is incredible slow to open, respond to any activity in it, and save it. 

I have tried everything I could find online, from doing ctrl+end and trying to delete rows and columns, to saving as a different file format etc.  

I spoke on Microsoft live chat and the guy tried to repair and corruptions etc but there were not any. He couldn't explain to me what had gone wrong within the sheet that made it so big. I have added or done something which has caused it to go massive! The spreadsheet genuinely is not that complex and should not be that big at all!

He tried something to do with add-ons as well but that did not work.

Can anyone help with any ideas? 

I would really appreciate anyone that can help at all!

Thank you :).