Hello! Exercising and limiting your fast food intake from every day to twice a week is a great start! That's definitely a great step in the right direction!
I wouldn't say you have to go straight in to the diet and exercise regimen of someone who's been living that way all their lives. In fact, that's probably not even healthy for you. For a very small case in point, I refer you to my experience. I jumped right from "sedentary" to "exercise six days a week," and in the second week of doing that, had to go to the doctor to find out those sharp pains in my calves were pre-stress fractures. Don't do that.
My advice would be, first of all, not to give up!! It's so discouraging not to see any difference after a month, and I want to congratulate you for coming here instead of throwing your hands in the air. The most important thing is to stick with it! Second, see if you can slowly work yourself towards more days of exercise and less days of fast food. Maybe you can start by adding more vegetables to your diet, or cutting something else that's processed or heavy in sugars/oils/whatever from your day, or (as those above me have very wisely pointed out) making your portions smaller. See if you can get yourself to one fast food meal a week, then one every two weeks, then one a month, etc.
Maybe you could even try making your favorite fast food meals at home? If you can find a recipe that gets close to what you want it to taste like, you'll be able to cut a bunch of the chemicals and processed ingredients they're using. You can put less salt on the fries, more vegetables on the burger, etc. That way, you could still be getting the satisfaction of eating your favorite meal, but without all the addicting ingredients they put in the fast food to try and coax you into buying more.