I doubt she is ill, I think she has "nipple confusion".She has had so many bottles that she doesn't want the breast now. I also think that she may have reflux, (and 50% of babies with reflux are intolerant to cows milk, which is what formula is made from....) and I also agree that 5oz is a HUGE bottle for a 3 week old baby, she must be stuffed, no wonder she's crying!!
Can I ask, when you were in HDU, where was she? And how was she fed? If she was given bottles and dummies from the start then she will have learnt to suck an artificial teat, which is totally different to the way they need to suck to breastfeed. As such she may well be sucking and sucking but not really getting much, hence the need to feed constantly. This can do bad things for your milk supply, as this kind of inefficient sucking doesn't stimulate the milk supply, so your milk supply goes down, baby wants to feed for longer as they get even less, and then they get given a "top-up" bottle, and of course get filled beyond full, and so on.
Stress can interfere with milk letdown, and a PPH can make milk slower to come in. Have you tried feeding in Biological Nurturing positions? Basically you lie on your back or recline, with baby laid on her tummy on your tummy, head between your breasts, and allow the baby to root and find the nipple, with minimal guidance. Many babies don't like to be held in the cradle hold, especially if you are holding the back of thier head/neck, and arch back, flail thier arms and cry when feeding is attempted like this. Try the baby moon thing with her laid on your chest on her tummy, rather than you lying on your side with her laid next to you.
Babies can't regulate thier intake until they are about 8 weeks old, until then they will guzzle bottles even if they aren't hungry because the milk comes out even if they aren't sucking, so just because she drinks a 5oz bottle doesn't mean she was hungry for a 5oz bottle. At this age 2 or 3 oz should be fine, bear in mind her stomach is the size of her fist, so little and often is the way to fill a tummy that size.
Phone a BF helpline;
The New National Breastfeeding Helpline 0844 20 909 20 ,
Breastfeeding Network 0844 412 4664
NCT BF supporter line 0300 33 00 771
La Leche League 0845 120 2918
Assoc of BF Mothers 020 7813 1481
Don't give up, you can still solve this if you get the right help and support. Good luck.