ettore on "4 months old - eating too much? Passing some poop with gas - is that normal?"

Hi ladies,
I have several questions about BF - my DD is eating very well (DS is a separate story - he only takes EBM from a bottle and in small portions, but we gave up and just give him what he takes when he can take it), but she can hardly ever wait three hours between feedings. She is a real fatty! And she is really good at getting milk even out of the pumped out breast. What worries me is that when she passes gas there is often a bit of yellow there. I end up changing a lot of diayoungihms because she immediately lets me know that she is not clean.
Is that a sign of diarrhea or is she just eating too much?
She is getting really really orotund.. I have to take care to clean the folds on her neck, because when she spits the milk gets there. She hates that of course. I guess it's good to have a plump baby, I just hope that it does not mean that she will have issues with weight later. But many sources say that it's impossible to overfeed a breastfed baby, so I would not worry if not for this pooping issue...
I remember that someone posted about a book that warns about problems that can come from feeding on demand, could you tell me more about it?
I am afraid that I am overfeeding her.
Also someone mentioned that babies with allergies want to eat often because their tummies hurt. Do you have any advice on how to spot allergies? She seems to be happy baby otherwise, no rushes , only reflux issues.
Thank you!!!!