Did the doctor say it was normal to gain only 8 ounces in 3 weeks? Seems a little low. My son was born 6 pounds even.. now at 5 weeks old he is 9 pounds 8 ounces. Drinks 4 ounces every 3 hours

Try paced feedings.

There is a growth spurt at 3 weeks then again 4 to 6 weeks then they eat more hun xxx

The guideline for a 3 week old is 4 oz 6 times a day. However my son was on 5 oz at 3 weeks. He is still on 5 oz now his bottles have just been reduced. From 4 to 8 weeks the recommended guideline is 5oz 5 times a day. However that's all to do with the average weight of the baby. My son is an average weight! Maybe you could try switching to hungry baby milk? As the baby gets older there are other alternatives too, like putting rusk in they're milk (my partners parents had to do this with him, which was advise by their doctor) obviously don't do anything until you talk to your doctor about it, but at 3 weeks my son was pretty much the same. He's 5 weeks now and much more settled into a routine etc, I think sometimes it's just them getting use to everything :) 

At night my baby could eat every 1-2hrs at times. I'm starting to go with the flow a bit more, and feeding her on cue. I find that she is a pretty good control now of what and how much she wants to eat. But she definitely can eat more at night, oh and when she first wakes up. 

My 4 week old girl was 7 lb 14 oz at birth. Her doctor said as long as shes gaining 1 oz per day then its good. At 2 week old she could easily drank 3 oz from bottle but always choke from drinking without stopping. We had to switch to a slower bottle nipple so she wont choke, plus we felt that 3 oz at that age was too much for her. Sometimes baby dont know if theyre full or not, they just keeping drinking. Now at 4 week she still drink 3 oz every 3 hours.