Something that worked for me... for 8 months I put myself on a strict diet (not necessarily what I ate) but when I ate... I made sure to eat 3 full meals at the same time EVERY DAY... breakfast, lunch, dinner... which is hard for me because I sometimes eat 1 big meal a day or something stupid...
But I ate 3 meals a day at the same time everyday, lots of protein and good fooda... potatos, meats, beans, eggs, drank a lot of milk, etc... and I worked out everyday or every other day (just stuff you can do without a home gym, even though I have one) like pushups, sit-ups, dips, pull-ups, etc... and after several months I really gained some progress.
Thats when I went from 125 to 148 in 5-6 months. Since then I have started slacking off again, Im not eating at regular intervals and im not working out as much and im slowly losing some of it again
What I said really worked for me, if you really wanna gain weight just get in a good routine, Im one of the hardest kinds of people to gain weight trust me on that! Also I once went on a 4,000-5,000 calory a day diet and that worked too but its hard to maintain such a large diet (weight gain supplements make it a lot easier since you can get 2,000 from that alone with a couple servings)
doing strength training excersizes makes a huge difference too since muscle weights quite a bit and is very dense stuff. Even if you dont have weights the stuff I said works but you need to push yourself not just do a few and keep increasing the amount occasionally!
Im not fitness adviser or trainer im just saying what worked for me, and Im positive we are the same body type...