I’m going to make a guess that the “stupid diet” was overly restrictive and cut your calories too low. Maybe a juice diet or a 500 calorie diet?
Since I don’t actually know what the diet was, I can’t tell you how your body is responding exactly, but I will make an educated guess that your body is in conservation mode. You have deprived it of the nutrients it needs (Fats, Proteins, complex carbohydrates, fiber, minerals etc…) and now that you are eating healthy, your body is hoarding all the nutrients it was deprived of.
Keep active, keep eating healthy, keep track of your nutrients and note the changes you see in your diet, activity level, sleeping habits and body measurements. It can take weeks to months for your body to fall into a habit/pattern. You may have abnormal menstruation, abnormal sweating, different body scents or other indicators to show that your body is adjusting to your new healthy lifestyle.
Stay patient and stay the course. Eventually your body will stop holding onto all the nutrients and water you take in now. I promise.
If this pattern continues, seek out the advice of a physician. If you were on your “stupid diet” for too long, you may have permanently disrupted your hormones and may require medication to fix it. Be aware, keep notes and don’t lie to your intake tracker. If you eat it, note it.