can't put on weight/ stomach problem

hi. i have been an underweight male my whole life. right now i am 6' tall and only 130 lbs. i have also noticed that ever since i was young i always felt like i was full in my stomach. i have discovered that eating lighter helps the feeling of fullness go away, and hopefully the feeling will be completely gone soon. I was wondering if this full feeling could have been contributing to not being able to put on any weight from the food I eat. If anyone can help me that would be great. Thanks in advance. Tweet