I am 36 years old.4 kids and I only weigh 115lds. And I'm 5ft 7in. Tall.I have never been bigger then 135lbs.I have looked on line and found that I am to be 135lds. I do no I don't eat right or sometimes not at all.for some reason I don't get hungry.I mite eat 500 cals. A day and that's it.the dr said I'm fine I gain 4lds in 3 years.he said that as long as I don't get lower then 100lds. I will be fine. I don't think so there is something going wrong some were in my body.I go go all the time running the kids here and there. House work and yard work I don't really slow down till 11:00 at night and I have to take something to sleep then or I will still be up doing something in the house.the weird thing is my hole family is very over weight sisters and mother & father.but me you can see my ribs and my bones stick out I hate it.there is no way I can slow down so any thing that I can do on the go to gain weight please tell me how.

No, you aren't fine if you are only eating 500 calories a day and expending so much more in your daily activities.

I bet you are taking in more than perhaps you realize. Try keeping track for one week. Use one of the calorie counters online to keep a record of everything you eat and drink.
You may want to ask your doctor for a referral to a nutritionist/dietician as well.

What are you taking for sleep and how long have you been taking it?

Keep in mind that the weights shown on the online height/weight charts are not an exact science... one size does not fit all. There are a number of factors that can go into weight. Some people naturally burn through the calories faster than others.

You can help by building lean muscle. You are busy, but you can make time to workout at home. During commercials is one opportunity to use some free weights. While the kids are doing homework. After they go to bed. When you first get up in the morning. While they are at school.

Plan your meals and snacks... sit down with your kids and eat at least most of your meals as a family. You can boost your caloric intake, and get extra nutrition, from the many dietary drinks available... such as Ensure, Boost, etc. as well.

I also wonder if you need your thyroid checked. A hyperactive thyroid can keep you from gaining weight.

I have had my thyroid checked 3 times in the past 5 years. And the Dr tells every time its fine.I do cook large meals for my family but the hole time I'm cooking I'm eating then I will sit with the family while they eat just so I can see how there day went and just talk.I did go and get something for me to wright every thing down that I eat or drink.I have got the ensure cause it does have more calories then the others.maybe just righting every thing down will help.I take a over the counter sleep aid the Dr has said that don't have anything to do with me losing or gaining weight.I find myself looking on line for the calories that I eat or drink if its not on the label like my coffee with cream & sugar down to the t spoon.