Looking to gain weight, instead I lost weight since going Primal
I'm 19 years old, male. I'm relatively short (5'8). I was always very skinny, but I ate lots of bread and other grain products. I've been doing strength training since 4 months, but since eating primal (more than a month now) I dropped from 132 to 125 pounds. I believe I haven't lost any muscle mass, if anything I slightly gained, but my goal is to gain, not to lose weight. I'm looking to get to 140 pounds, at least.
Important to note is that I'm really active. Since starting primal I dropped running, but I've since started to take long strolls (1.5h +) every other day, besides cycling to college 5 days a week (1 hour / day) and walking or cycling any such distance, to friends etc.
My current diet is very primal: lots of biological eggs, meat products, nuts, vegetables, fruits. I dropped every sweet besides (sometimes) chocolate. I do eat quite some dairy: cheese, milk and quarck. All I drink is water and milk.
Bottom line is: what can I do to gain around 8 kilos (18 pounds) of muscle mass? I already work out for 30 - 40 minutes every third day, and I've really seen my muscles take shape. Yet I won't really gain weight. I think I mainly need dietary tips.
Thanks in advance!