If you have been skinny all of your life no matter how much you eat, you probably are programmed that way by genetics or high metabolism or both.
You may be working out with weights but not making any progress at getting bigger.
Consider that you are a hard gainer and may be going about it all wrong.
If you lift weights like bodybuilders, expecting to get big like them and you are a hard gainer you are wasting your time.
Your genetic makeup will not allow you to get bigger using those kinds of programs, you will get stronger but not bigger.
As a hard gainer you must take a very different approach to gaining weigh and lifting weights.
One very key thing you must do is start eating much more food than you are now.
If you do not increase you calorie intake you will not get bigger.
You must take in much more than the calories you expend.
For the best success you must spread your meals out to about 3 hours apart if possible.
You do not want to keep eating constantly through the day or you will overload your digestive system.
You need to give yourself time to digest some so your body can intake the nutrients.
As far as lifting weights you must lift heavy.
Only do basic movements like bench press, overhead press, curls and squat.
Do these with a barbell only and keep trying to add more weight.
Workout only three times a week, doing the squat once a week.