Hi & Welcome. Yes, headaches and weak bones are both documented side effects of taking Dexona (Dexamethasone). You need to immediately stop taking the tablets. Dexona Ciplactin is not recommended for weight gain. It is very commonly misused due to advices of unqualified doctors. Dexamethasone is a steroid. It has many side effects like diabetes, increase BP (hypertension), weight gain, depression, moon like face, hair loss, thinning of the bones, muscle weakness, stomach ulcers, skin stretch marks, delayed wound healing, acne, and sex-related side effects Ciplactin contains antihistamine Cyproheptadine. This is taken as an OTC in some countries as it can increase hunger but this drug has many dangerous side effects like drowsiness, increased heart beats, dryness of mouth, constipation and retention of urine. So, in view of the above Dexona Ciplactin is a very dangerous drug and you should not take it at all. In order to gain weight properly, you should meet a dietitian and take a diet plan which is perfect and standard way of gaining weight. You are not categorized as underweight you are just borderline. You may appear thin and might want to increase weight. Wishing you good health.