How do i get my daughter to eat food and gain weight

I have a 16 month old daughter who seems fine to me, but is under weight by medical standards. She has always been a great sleeper and very active child who has met all of the child hood mile stones before due time & she is very rarely sick. She is a grazer when it comes to food and is quite picky to, she has been lactose intolerant from birth and gets eczema + plus a big pain in the belly when i use to feed  her dairy or lactose. It took me lots of trial and errors to work that out.  
Is it possible that she has developed a fear of food? Due to the history she has with lots of stomach pain.  I have tryed different feeding methods but my daughter will go all day with out food and demand milk. So i give her 240 mls of milk per a bottle and she may drink 3-5 bottles per a day plus graze on food all day or not. (the food that is) I sit her down for three main meals that can take from 15 minuets to 1 1/2 hours to eat.. Food seams like a game and a novelty to her. If she can poke a hole through the food she will not eat it and she will only feed herself with utensil or hands.She puts the food in her mouth chews it then spits the food out all the time. If she dose not want to eat she wont eat, i have no hope in hell of butting heads with her over the matter & it just turns into  her screaming at me. Im a bit over that part now because i have been putting up with this for over eight months!
What can i do to help this situation?
Im trying my best to make her eat healthy food, my husband and i are big on food and meal times. it's like she has no interest in eating food at all, its like she has better things to do with her time like playing or something.

Every one says she will grow out of this but when will that happen? Is there something more underlying with her heath? Should i be referred to a pediatrician? can they help solve this eating mystery?
Look, i see a healthy child who has fussy eating habits, but needs help from a Dr's point of view.....

[Renee Radenberg]

Her weight is just above the 5th percentile and her height is just below the 75th percentile for her age. She probably appears thinner then she is due to her height. Suggest switching to a sippy cup, from the bottle, for fluids (including the milk you give her) so hopefully she will eat food instead of wanting the bottle. Try nutrient dense drinks, such as Pediasure (which is lactose-free), instead of the milk for extra calories and protein. You can even make milkshakes (pediasure and soy ice cream) for additional calories. She may need to be taught how to chew and shallow. It is a learned skill. Suggest getting her evaluated. Hoped this helped you.