Muscle, strength, stamina. Whitening.

I am 24 and 50 kg. So highly underweight. Want to gain muscles without going to gym. Can you please suggest me some ways/exercises and relevant diet to gain weight. I have been underweight all my life. And I also have digestive disorders like stool formation problems e.g., (1) sausage-shaped but lumpy, (2) like a sausage but with cracks on surface, (3) soft blobs with clear cut edges (4) fluffy pieces with rugged edges, a mushy stool , and sometimes (5) the ideal stool- like a sausage or snake, smooth and soft. I have to pass stool 2-4 times a day. The other problems are IBS- inflammatory sensation while passing stool, malabsorption, lactose intolerance, gas formation and farting with burning sensation after eating chana daal, rajma, milk products except curd and ghee, non-celiac Gluten sensitivity, restless leg syndrome, spinal pain when sitting without back support, hair loss and whitening.