Help! to Gain weight.

Hello. I'm in my late 30s and have a 7yr old. All my life I have been under weight,
I am 5foot 4 and weight between 7 and 7 1/2. (101lb) I've use this app and I'm
amazed to find I only eat 2/300 Cal over, every other day and 2/300 under in-between.
I just can't eat that much every day, I don't fancy food, feel sick because I'm full all
the time. Everyone says I'm lucky and so no sympathy,which I don't want, I just want to
be able to buy clothes and put on a stone or so! I hate the way I look, clothes hang on
me and I don't feel like a women or a adult. I hate getting dressed and summer has been
horrible because I'm getting so down. Food and my weight is in my head every
second, its driving me crazy! Sooo that's me, I sound like a right Moody cow, Im not!
I'm lively and fun but this is taking over my life. I've stopped using the app because
I was getting down eveytime it said 'in 5wks ur weight 102lb!!!
Any advice? I'm so envious of anyone over weight. xx