I have always been underweight and found out that being gluten intolorent was the main cause, now i am on a gluten free diet and im trying to gain weight but havent been very sucsessfull, does anyone have any suggestions on ways to help me gain weight?

You may naturally gain weight as the body heals. Take a good mulitvitamin. Get plenty of calories from healthy sources and plenty of healthy fats and protein. Have some protein with every meal. Olive oil, avacados, nuts, nut butters, even eggs and full fat dairy in moderation are high in calories and good for you. I have full fat yogurt for breakfast. Macadamia nuts are very high calorie. Avoid trying to gain weight by filling up on processed/highly refined carbs and sugary things. Those are fine in moderation but balance is important.