How do I gain weight being type a?

I am a slim 20 year old male and weigh about 116 lbs and stand 5'8" tall. I would like to gain 15 lbs. I haven't been following the BTD, but will be now. I usually eat a lot of rice, bread, fruit/veggies, but I can never gain weight. I also have eczema so what could be triggering it. I have elimated all dairy and Sugar from my diet, except natural sugars from fruits. Any advice would be appreciated thank you :)