Losing weight too quickly

I am 5'8/5'9 and 207 lbs and have lost almost 22lbs thus far. I started actively counting my calories early May but have been reducing portions since early April. I have my diary set to lightly active and to lose 1 lb per week which has me eating roughly 1900 calories a day and I typically eat back my exercise calories when I exercise. This is super easy to stick to since I've started being smarter about what I eat and am opting to eat more nutriously (with splurges mixed in). However, I am starting to grow concerned as it is becoming harder to eat up to my calories and I am losing weight at almost 2lbs per week. I don't exercise regularly but have my activity tracker synced to mfp and negative adjustments on. I am concerned that I might start metabolizing muscle mass if the weight loss doesn't slow down. Should I be concerned with this? What is a good nutritious high calorie snack that can help me meet my calorie goals?