As someone who has been through the P90X programs multiple times, the V-Diet, and multiple workout programs on this website over the past few years, from my experience the best thing I did for my training was get out of my living room and into the gym, started cooking/preparing all my meals, eating clean and lifting heavy. As Chris said, the P90X workouts are mostly metabolic and conditioning due to their hi rep/low rest nature, but you’ll peak eventually and stop making progress.
There’s only so far body weight exercises and 50lb dumbbells will take you. They feel grueling and can add some definition for sure (if your nutrition is in line,) but from my experience at least I do not think the P90X workouts make good long-term programs.
The V-Diet workouts are not at all similar to the P90X workouts, possibly with the exception of the V-Challenge, but there’s a reason that the V-Challenge is only once per week. It’s a metabolic boosting, fat torching workout, ensuring you’ll melt the fat off to get the definition you desire. But, the rest of the workouts are weight training centered, having you perform the set until form and tempo start suffering, so definitely not to failure. That’s the beauty of using the V-Diet with the V-Workouts, they’re a perfect match. Have you tried doing them together previously?
Maybe consider Chris’ suggestion of metabolic damage more seriously; 7 weeks of high intensity P90X workouts combined with improper nutrition, (also not sure what your sleep schedule is like), could very well be putting you on that road.
If you “always end up back where you started,” you clearly need to change something about your habits. You are headed down the right path with working on your nutrition, as you said, you need to “find a way to stop eating processed foods and start working on preparing your meals.” That’s a serious life style change, and also essential if you want real progress. If you’re motivated enough, you’ll do it and never stop.
You say you have “small changes” in your physique, if you want BIG changes in your physique, get into the gym and start lifting heavy. There are a ton of fantastic programs on here. CT’s Indigo-Hypertrphy workout was the first program I used in the gym and it was the perfect program to build foundational strength on the big lifts and get serious muscle growth, once you start you’ll never look back. Good luck!