Hi,
This is such a difficult area. If only we had that crystal ball that told us what is really going old. I don't quite understand why the dr thinks your milk would be low? Milk supply works on supply and demand - the more you feed the more you make - and it sounds like she feeds frequently. Am I right in thinking she's 7 mnths old? At this age your baby need for rather than formula. Nutrition for babies and young children is different to adults. Fat has twice the calories if carbs and protein - and while adults are advised to steer ear of fats good fats are nutrtious for babies. Dairy is great for adding calories. Butter and cheese are great - try adding somecheese to her maser potatoes. Yoghurt is great and just because you need a spoon doesn't mean it's not babyled solids.
Does your lo have any signs of allergy? Eczema? Ashma. Any in the family?