It's really impossible to say unless you can give us LOTS of details about EXACTLY what you are doing, and example photos.
i normally edit my photos in photoshop only but now i've stared using the lightroom cc. I start editing in lightroom then carry on in photoshop. after that i save as a JPEG file. when i look at the photo on the Mac it looks great but when it's on the online portal it looks like the colours faded. For some copyright issues i won't be able to post any photos as they are for clients
One possible reason this happens is that when you export from Lightroom, you did not select sRGB as the color space. Please check that setting.
If that's not it, Can you show us with a non-copyrighted image?