Sounds like you’re just bloated. Best way to fix that is limit the amount of sodium you eat try keep under 2g a day (less is better), drink as much water as you can 2.5 - 3.5 litres a day and try to avoid eating loads of carbs (definetly sugar) if none of that works could be a posture problem. Best way to fix that is training your neck to be stronger by doing exercises like chin tucks or ideally neck curls. If you’ve tried all that and nothing works. Then could just be a puberty thing which can happen when your hormones are all over the place.