Had quite normal weight but wanted to lose weight and was making 20 hours interval between meals.i got very skinny.could it cause my hypothyroid?

Hypothyroid: Could be but that is not your main problem. Making 20 hours interval between meals is not very smart. You need to take a proper diet. What is your height and weight? Please go online and look up "Body Mass Index" (BMI). That will tell you what you need to know about your weight.

Losing weight: I commend you for being concerned about your Health! Stress of personal appearance, self-image, relationships and approval of others can cause weight loss. It is unlikely that losing weight will cause Hypothyroidism. Hyperthyroidism can cause weight loss. See Endocrinologist, Psychiatrist and a Gynecologist for diagnosis, review of medications and procedures; and collaboration of treatment.