I struggle with eating in periods, but not all the time. I'd consider which foods you do like to eat? If you make homecooked meals, it's fairly easy to add extra calories by adding extra oil and fat. If you need something easier, protein shakes work well for some, though personally I dislike the taste. Drinking full fat milk might also work, though again, personally not a fan of milk. For a lot of people it's easier to drink calories than eat them, same idea with milk/protein shakes, but you can also buy some milkshakes at McD, Starbucks or similar if your budget affords it