The puffiness overnight is due to water retention. Cut back on your sodium intake and drink more water, since it will flush your system out. Sounds odd to drink more water if you are retaining water - but your body will hold water if you are getting dehydrated.

The weight can be a part of aging. A person in their 20's can eat anything and not gain weight. As the decades progress people begin to lose the ability to metabolise the way they used to. As muscle mass decreases, your body will not be working as hard as it did previously. Muscle takes more energy (calories) to burn.

If you are very concerned, please see a doctor and find out why you are having these issues with weight and water retention.

Good luck!