My BDD questions

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I don't know if anyone will see this, but I really need to talk. I've had anxiety forever, but about a year ago I developed BDD. When I look in the mirror my stomach is huge and the rest of me is grossly skinny. My mom says that I need to gain weight being that I weigh 114 at 5 7". Do you think that's underweight for my height? Also, every time I'm out of the house I'm always focusing on how much skinnier other girls waists are. Does/has anyone else do/done this? My parents both tell me my waist is skinny, and I've measured it to be 25 inches. Do you think they're lying to make me feel better? Do you think a 25 inch waist is skinny enough? Right now I've been trying to gain weight back to my original weight of 118, but I think it's all going to my stomach. My mom says I'm seeing things, so I guess my last questions are: is 118lbs too heavy? Can you gain weight in only your stomach if you're eating healthy? And can I really be seeing something that isn't actually there?