For your height i'm thinking 106 might be underweight? If that's the case then you don't need to feel guilty for gaining..but rather feel happy for your health. Take it one step at a time, perhaps find your healthy BMI (and weight at which it would ocurr) and aim for that. Eating more and having less energy..i don't know much about this or about you but it could happen with depression or any other kind of mental strain. You said you're not under stress so, maybe it's something subconscious having to do with your boyfriend's diet?

just trying to offer some hopefully helpful ideas...good luck.
*lil