I've just mentioned this in another post so my little book is open at the right page.
The Pocket Guide to Breastfeeding and Human Lactation (Riordan and Averbach) says:
Average infant breastmilk intake:
Birth to 24 hrs: quarter oz
24hrs-2 weeks: 1 - 1.5 oz
2 weeks - 1 month: 1-3 oz
1-2 months: 2-3 oz
2-4 months: 3-4 oz
4-6 months: 4-5 (It stops there).
Because of the way breastmilk is digested more efficiently (hence breastfed babies poo less then formula babies after they're a few weeks old) the quantities of breastmilk are smaller than what you would give a formula fed baby.
However this is an average!! So there are bound to be babies who need a little more and perhaps your LO is one of them. It sounds as though he was dissatisfied by what you were giving him and you naturally responded to this and made an adjustment. I wouldn't worry about overfeeding him unless your doctor/ health visitor is concerned he is putting on too much weight. Ask your doctor for advice on this. Plenty of people have the opposite problem to you and are concerned about not enough weight gain. Try not to compare him to friend's babies - everyone is different.
I also wouldn't worry too much about him drinking inconsistent amounts as he is getting quite a bit over the whole day. Breastfed babies also vary their amounts during the day but mothers feeding with the breast just can't measure!
this morning I can only get 2.5 oz and it has been with great struggle.
If this is his first bottle after a long interval I can see why it might seem strange. See how the pattern goes. Did he feed OK later on in the day?