exactly this - eat more
you're only eating 2 solid meals a day! Most people on this site would eat more while cutting, never mind bulking.
bump up to 4 solid meals, replace a couple of shakes with something solid.
And when you do have a shake, dont just make it whey.
Quick recipe for loads of kcals:
2 scoops whey or casein, 1 or 2 tbls natural peanut butter, banana, 50-100 gr rolled oats
700-1000kcals right there dependant on whether you add milk or water
Play around with the ingrediant if you want but the point is its not hard getting enough kcals, just make sure you're eating most of them. good luck!