So you're saying you're 5'10 and about 103 pounds? In the US most of us aren't great at metric system, unfortunately, but this is what I think you're saying. That's incredibly light. Have you seen medical professionals about this? Do you eat? Have you always been extraordinarily thin, or did you have a late growth spurt that left you much taller but not at all heavier? The basic way for most people to gain weight is to eat more. If you don't care if you gain fat or not, you can do this more quickly by eating lots of fatty foods and sugar, but that won't be healthy. If you eat more meals a day or just eat more of the healthy foods you eat normally you should gain weight. But to be that thin, either you have a genetic heritage in your family or your metabolism might be extremely high. Protein weight gainers are actually made for people wanting to add muscle, usually. They're generally not very healthy, and only work if you're doing a lot of weight lifting. But because most of them contain a lot of sugar and some a lot of fat, it's possible if you add them as an additional meal you might gain some weight, but you can do the same thing by eating more and eating more frequently. But that's only assuming there's not something wrong with your metabolism or something else, because if that's the case the answer might be dealing with that, not you're diet. You might, for example, be nutrient deficient or the opposite, too much of something that is affecting your metabolism. Which is why the first step is to see a medical professional to see if something is up.
I have two kids. One was low weight to begin with from birth, the other was not. This has continued their entire life. One is just naturally very lean and has a hard time putting on weight. He eats. He's overall pretty healthy. But is scrawny. He's been actively trying to put on weight, it's like a job! Our doctor always says that our son is 'normal' even though he is low weight because he is following his own growth chart. So, I don't know where you stand with that. If this has always been the case for you. If this is new? That is a different situation.
Have you ever had your thyroid checked? Hyperthyroid can make someone abnormally thin. Simple blood test checking thyroid levels can determine that. Normally there are other side effects as well though. I do think you need to talk to your doctor to make sure this is not a health problem underlying the cause and if there is no health problem, you can focus strictly on how to gain weight. Otherwise, you want to combat the underlying health problem. Let us know what happens. Here's a helper article on gaining weight healthfully. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/underweight/faq-20058429