Any nutritionist can tell me the best foods and habits for weight gain? Or some natural medicine that help me with health.

Gaining weight. Gaining weight can be difficult for people who are naturally thin. Engage in exercise especially weight training to help develop muscle mass, eat small meals but every few hours, eat more lean protein and healthy grains. There are no great pills that help with weight gain unfortunately. I personally think we are better off being thin than heavy.
Nutritionist is best. If you are concerned that your diet may be inadequate or you need help losing weight a nutritionist can be very helpful in helping you meet your goals. While "natural" supplements sound healthy, be cautious especially if you are taking precription medications. Dangerous interactions can occur. Remember to share information about all supplements you take with your health provider.