HELP! Issue with font changing constantly overnight.

Hi all, I'm having issue with a website that I am working on which I have never come across before and it's becoming increasingly frustrating. I can't figure out why for the life of me it keeps happening!

I set the font sizes/styles etc for the website, but for some reason the size keeps changing on me overnight. I work on the website one day, save my changes and then the next day the font has changed to either too small or too big - it's like it's resetting itself. It happens if I've just been working on content not even adjusting font sizes or whatever. But it is very frustrating! 

Any advice would be much appreciated!

This sounds like a caching issue, have you tried clearing your browser cache?