1) Why are you doing 5x5?
2) I'm not sure if there's anything unique that I can tell you besides that you're going to have to get used to eating to the point of being uncomfortable. Ed Coan, perhaps the G.O.A.T of powerlifting, told me he had to "eat cleaner" to gain weight because all the weight gaining shakes and fast food filled him up too quickly. I would recommend eating single ingredient foods every 3hrs (set your alarm). Have a good hunk of protein, something starchy, and a big glass of whole milk (+/- lactase pill if you don't drink milk regularly). Chicken/beef/steak/rice/oats/eggs/yogurt/milk/peanut butter and jelly sandwiches/pasta/etc.
3) There are no secrets/shortcuts...really.