As for the others, telling someone to eat more is the worst advice one could ever give, unless the goal is to get fat.
With that being said, it's ok to eat a lot when breaking your fast. You could afford to gain some weight anyways. I would just lift some weights a few times per week just in case. That way if you gain a bit hopefully it will all be muscle. If fat gain occurs, you have to cut your calories for a while to drop it.
At 5'8" I wouldn't let your weight go above 160. So you clearly have some room for growth, but just don't go too crazy.
Not sure if this was directed at me, but notice how I said "lift heavy things and eat more"
Lifting heavy things requires eating more to produce results. Everybody can benefit from increased strength.