Are you working on a JPG file and then saving it again as a JPG file?
If so, that will degrade the image each time you save it.
JPG is a 'lossy' compression format so, each time you save an image as a JPG file you lose a bit of information, no matter what program you use. It's a bit like photocopying a photocopy of a photocopy. Each time the image will get worse.
Best to work on images as RAW or TIF files and only save them as JPG as the very final step. And, if you need to make any further changes, go back to the original TIF file again.