I've had that problem. I used to be significantly underweight, quite a few times in my life. My hormone levels are low, so I have to be on birth control to even things out. Now I have no problems gaining weight lol. I've tried to go off a few times, but I just can't.
2c-3a - coarse - normal-high porosity - high density - growing out to donate

NP/LP: KMF Whenever Conditioner/ YTCucs
RO/LI: Sevi Pumpkin Seed DC / CJ Argan & Olive Oil, KCKT, YTBbs
DT: Coconut Oil + scalp massage
COLOR: henna, amla & indigo