Toddler won't eat

So I'm really fustrated because I just had a baby and I have a 18 month old baby girl up she is very picky and I am worried she's not getting what she needs and she is fussy all day because she is hungry she like oatmeal and tomato based foods but the last coue of days she has been throwing a fit throwing her food because she doesn't want it and I don't wanna just feed her junk what can I do I am going to speak to her doctor Monday but has any other mom gone threw this