The trouble with just cutting down on what you eat is that you can sometimes eat more than you thought you were. You only really know if you are eating portions that will make a difference, if you monitor. But cutting out 'junk food' is a good start. Often it is achieving a lot of little gains rather than looking for one big issue, that makes the difference.
IMO you have to do a lot of exercise to burn off a small amount of food, so if it is pure weight loss you are looking for, diet is where to concentrate. And keep in mind that if you are forcing yourself to do something you don't like (and don't believe you will stick with after you have lost the weight) then you'll be back as you are now a few months later. You need to find a better diet/exercise regime that you can get into the habit of, and which suits you.