A new week is a good moment to get back into your rhythm. After a weekend of good food and rest, you don't need to make up for anything. You just need a small, clear goal.
Pick one that is easy to say out loud: three gym visits, two swims, or 20 minutes on a cardio machine. Write it down or tell a friend, so it feels real. Then start today instead of waiting for the perfect day.
Keep it simple and kind to yourself. If a day doesn't go to plan, just carry on with the next one. When Friday comes, look back at what you did and enjoy the feeling of keeping your word to yourself.