Could be your routine not your diet (No it couldnt, gaining weight is down to cals in V's cals out, if you stop gaining weight it is down to diet, ie. nt eating enough) , when was the last time you switched your routine up?
If your trying to gain weight I'd cut a couple of those cardio days out imo, but thats up to you.
Also check out this article I found it very interesting.
http://www.bodyrecomposition.com/mus...ass-gains.html
Not saying what your doing is wrong, but I used to eat very frequently like you do. After a while I cut back and started eating only about 4 times a day, but made sure my calorie intake was still above maintenance, and I noticed my gains started to do better. Your body could get used to a certain type of nutrient intake spread throughout the day, switching this up might help, kind of like switching up a routine.