Sounds to me like you're under eating.
You claim "I exercise and eat little". How little?
If you're not getting enough protein in your body each day to build healthy skin, hair and nails, they will show it.
Gaining more weight if you eat any more is a common thing if you're under-eating. If that is the case, you've trained your body to get by on too few calories and that it's starving. When you give it extra calories, it gets by on the too-few it's always used to, and turns those extra ones into extra fat storage, because you're starving.
It takes at least 6-8 weeks of eating a normal healthy level to kick this pattern and begin losing weight.
Can you share more about how you eat?
Deb, in New Zealand