I'm a bit underweight and i've been trying to gain weight but it's just not happening. I see a slight increase on the scale, but there's no noticable physical difference.

Most of the time, my stool is watery so I think that's called diareha. Does this mean i'm not digesting the food properly? Is there some kind of malabsorption problem or a bunch of tapeworms inside of me? I have a bunch of other problems like my hair lacks a lot of flexibility, which I heard is a symptom of zinc deficiency. Is my digestion system just incapable of digesting my food properly?